"It's not your fault."

"You did what you had to do."

"I would have done the same thing."

"Nobody would have expected you to trust him."

"It's dangerous to trust anyone too easily, let alone an old enemy."

"There's no shame in being wary of whom you trust."

His friends and the letters that came from Berk as soon as he sent word all said the same thing: that Hiccup shouldn't blame himself for not trusting him. His father, Gobber, Heather, Astrid, everyone agreed that it would have been foolish to believe what an old enemy said about anything, that no Viking would have expected him to act differently. What had happened was tragic, but there was nothing Hiccup could have done to prevent it. Despite how things had turned out, he had done the right thing – refusing to trust someone wasn't nearly as dangerous as trusting too quickly.

Given what had happened the last time Hiccup had trusted an old enemy, he couldn't argue. He knew they were right. He just didn't have the energy to tell them it was irrelevant. None of their reassurances could make him feel any better because that wasn't the reason he knew this was his fault. Nobody understood just what a terrible mistake he'd made. He wasn't ashamed of the fact that he hadn't trusted Dagur but of the reason why he had decided not to trust him.

The truth was that by the time Dagur showed up at the Edge, Hiccup's first instinct was to trust him. He reminded himself to be on his guard, not to reveal too much, that there was still a chance the man could turn on them even if he didn't have some ulterior motive now, but it was like remembering your lessons on the day of a test, not something that came naturally. He had to actively hold himself back from trusting the former dragon hunter as much as he wanted to, and he succeeded. He kept him away from the base, kept their plans hidden from him, gave him the safest dragon possible. He did nothing that could put him or his team at risk, but he did it for the sake of duty and discretion, not from any personal fear of his own.

Every minute Dagur was on the island, Hiccup told himself he was a potential threat, but he obeyed the voice without believing it. True, he and Toothless owed the man their lives, so even if Hiccup hadn't trusted him, he probably wouldn't have alerted the riders as soon as he found him in his hut, but he would have forced him to leave and refused to teach him anything. Instead, Hiccup showed him Berk's greatest, most closely guarded secret, something Alvin had spent months trying to trick or blackmail him into giving him – dragon riding. It would be unacceptable, unbearable, unheard of for Hiccup to give that secret to someone he didn't fully trust.

It was impossible for Hiccup not to notice how his feelings had changed since the day he and Toothless had been shot down. Back then, he'd questioned every move Dagur made, everything he said, every offer of help he gave. Hiccup's first assumption had always been that everything his self-proclaimed arch enemy did was intended to betray, hurt, or kill them until it was proven wrong each time. Now, he felt safe enough to let the man support him when he couldn't walk, to leave him alone with Toothless, to leave him and his dragon alone with his friends. Had Hiccup stopped to think about it, he would have realized those were signs of trust every bit as strong as dragons allowing you to walk unscathed amongst their nests. But he didn't think about it at the time – he just did what felt right with no fear that Dagur would hurt him or those he cared about.

Astrid, unsurprisingly, was the only one who noticed that even though he was prudent enough to act like Dagur could still be dangerous, Hiccup didn't believe he was. She forced him to admit that, regardless of the precautions he took, he fully trusted the man who had risked his life to save him and his dragon. He felt guilty about it, knew his father and every Viking he could possibly ask would tell him it was unwise and foolhardy, but he couldn't deny it. In spite of the danger, Hiccup did believe Dagur had changed and deserved a second chance, and he was willing to give it to him and forget the past, even though he didn't expect or demand his friends (especially Heather) would as well.

If anything, Hiccup had underestimated the change in Dagur. When Heather showed up and Dagur realized he'd been lying to him all along, Hiccup had expected he'd be so furious, he'd go berserk again, decide no one could be trusted and swear revenge on him all over again. He'd been shocked when all the Berserker did was lament all the months he'd wasted worrying about his sister. Did he, like Hiccup, understand it was Heather's choice to see him again or not and that Hiccup and the other riders had no right to betray her wishes? What else could it be? If nothing else convinced all of them how much Dagur had changed, that alone should have.

It was no wonder that, when Dagur's reunion with Heather drove him to want to leave, Hiccup's immediate reaction wasn't relief but pity. Before, Hiccup had been desperate to get him out of there before he or Heather learned the truth; now that he no longer had to worry about that, Hiccup was actually sorry to see him go. He still had so much more to teach him... He didn't want him to lose hope because things hadn't worked out with Heather... Without the goal of finding his sister, what would he do now...? Where would he go...? In that moment, Hiccup didn't think of all the horrible things Dagur had put him through since they were kids; he thought of all the years he himself had spent as a lone outcast rejected by everyone around him, even for a moment by his only family. Hiccup knew how painful that was, and no matter how much Heather and Astrid insisted they couldn't trust Dagur, Hiccup trusted him enough to want to console him as a friend.

Why did that change? What unforgivable crime did Dagur commit to make Hiccup lose all faith in him?

He questioned his judgment.

Dagur had Hiccup's trust completely until he started warning him he was making a mistake by planning to attack Viggo's shipyard. This mission mattered more to Hiccup than any they had gone on since they'd met the hunters. He must have spent more time planning it and preparing for it than for anything he'd ever done in his life. If successful, they would cripple the entire dragon hunting operation; it would deal a blow strong enough to more than make up for the loss of the Dragon Eye and all their other defeats by the hunters.

It was a chance Hiccup had once thought he could only dream of – a large portion of Viggo's fleet all gathered in one place where conditions would enable the dragons to take them out in one quick strike. He had been nervous about the risks at first, but every day of surveillance that went by without the hunters catching onto them made him feel more confident. Viggo had no idea what the riders' next move would be. Hiccup was the master of the game now; after months of feeling powerless against Viggo and his meticulously constructed strategies and vast net of hunters and ships, he finally felt like he was the one in control. He would win this one – he knew it. Everybody agreed – the other riders were just as thrilled about the plan as he was. Not one of his friends had ever expressed a single hint of doubt about it.

After weeks of hearing nothing but encouragement and enthusiasm from all sides, to hear someone challenge his plans felt like an attack. Hiccup no longer saw the friend who had helped him escape the hunters but the Berserker chief who had kidnapped his father, tried to drown his friends, planted a herd of Smothering Smokebreaths in his village, tried to kill a man just to obtain the Skrill, joined forces with the most despicable men Hiccup had ever met just to get revenge on him. If he was really no longer their enemy, why would he try to stop them? Ruin their most important mission? Spoil the greatest opportunity they could hope for? Even at his craziest, Dagur had always been crafty – apparently, he was up to his same old tricks, trying to make Hiccup second-guess himself, double-crossing him the same way he had double-crossed Alvin.

The rational part of his brain was just strong enough for Hiccup to wonder if maybe, just maybe, Dagur was right, but it didn't take much for the others to assure him there was no way he could be. Hiccup was embarrassed that his confidence was weak enough for him to even consider that. How could he ever think Dagur the Deranged could spot a trap that he couldn't? Did Dagur really think he was smarter than him, after all the times Hiccup had outwitted him? Hah, he should try telling that to Viggo Grimborn. Viggo himself admitted that Hiccup was the only person he'd ever encountered who was intelligent enough to be a serious threat to him. Viggo knew Hiccup was more than capable of outsmarting him – hadn't he said so every time they'd met? If someone as arrogant as Viggo obviously was could say that so often, he must really believe it. It had always frustrated Hiccup to hear his new enemy compliment him on being such a "worthy opponent," but it couldn't compare to hearing Dagur imply Viggo was smarter than him! He had to prove him wrong!

"Use your brain, Hiccup!"

"I am, and you know what? It's telling me not to trust you."

He hadn't lied – he'd been wrong. Hiccup now knew it hadn't been his brain telling him that but his emotions. Otherwise, he would have remembered the time Dagur lured them into a trap by spreading rumors of building a superweapon and realized this was just a larger-scale version of the same trick. It would have occurred to him that a spy trying to ruin their plan would have either asked a bunch of questions and left, or encouraged them, offered to help, gone with them, and sabotaged it, not try to talk them out of it. He would have realized that Dagur would never let them lock him up without a fight if he truly wanted to stop them. If he'd been using his brain, Hiccup wouldn't have let himself get overconfident enough to overlook all the suspicious parts of the situation he'd had weeks to spot that Dagur had noticed instantly.

Logic would have told Hiccup that the set-up was too easy, too inviting, too good to be true, tailor-made to suit all his greatest desires for an attack. But he hadn't listened to logic or reason – he'd listened to his anger, his hatred of Viggo and the hunters, his desperation to cause them some real damage at last, and, most of all, his confidence in himself as the superior strategist. He hadn't wanted to believe he'd miscalculated everything from the start... which, no doubt, was exactly what Viggo had counted on. He knew Hiccup wouldn't be able to resist the opportunity he was giving him.

Had Viggo also intended for his flattery to make his opponent overconfident and complacent? Hiccup wouldn't put it past him. All these months, he'd acted like Viggo's constant praise either meant nothing to him or annoyed him, but at some point, he apparently started to believe it. He did believe he was smart enough to surprise Viggo, that nothing could stop him this time. In reality, he'd blinded himself to the obvious. He thought he was being careful and cautious when he was really being reckless. Even when someone spelled out what he was missing, he refused to see it.

Hiccup had been so determined to see his plan through to the end, it never occurred to him until it was all over that enemies didn't warn you when you were wrong; they didn't try to stop you from making mistakes. Hadn't his father told him that, as chief, the people he trusted the least weren't those who disagreed with him but those who agreed with him all the time? His dad had warned him, when he became chief, to beware of those who curried favor by agreeing with everything you said without question; people who deserved your respect would have the courage to speak up and disagree when they believed something was wrong. Hiccup's friends weren't shy about telling him when they thought he was out of line, but that never made him doubt they were his friends.

A spy would have made the riders feel as safe and secure as possible. A spy would have given Hiccup all the praise and approval he could to make him feel comfortable. A spy wouldn't have acted so obviously interested in their plans but pretended not to care. A spy would have let Hiccup believe he was on the right track, not try to make him examine the situation more closely. Dagur hadn't acted at all like someone playing a part, who wanted to gain your favor – he'd been unafraid to tell Hiccup something he clearly didn't want to hear. That was what true friends did. How could he not have realized that?

Because he was a Viking – he had stubbornness issues. Hiccup had been too stubborn to consider anything that might threaten his plan. He'd closed his eyes and ears to the truth and ignored the man who'd risked angering his new friend to protect him from himself, to warn him he was being gullible, to try to convince him he was putting himself and his friends in danger, to try to stop him from getting them all killed. Instead, he'd believed the voice in his head that had told him at the same time, You're ready. You know what you're doing. You're too brilliant to be tricked. Who is he to lecture you? You don't need his advice – you can handle this. He didn't recognize whose voice it was until it was too late. In the end, he'd chosen to listen to the flattery of an enemy over the warnings of a friend, and his friend had paid the price.

Hiccup couldn't help but torture himself with wondering how things would have turned out if he'd realized all this earlier. Why didn't he ask himself any of these questions before someone died? Why didn't he stop to think about it when he had the chance? How could he not have noticed what was going on? In hindsight, everything looked so clear. It was obvious whom he should have trusted. Nothing his friends or father said could change the fact that someone had died, not because of his lack of trust, but because of his blind arrogance. He wondered if he'd ever be able to forgive himself.

Hiccup confessed exactly how he'd gone wrong and why in a letter to his father. His dad wrote back, saying he knew how it felt to see someone else suffer because you'd refused to listen to them, and reminding him that you couldn't undo your mistakes, only learn from them. Heather and the others reminded him they hadn't wanted to abandon the plan, either, and had been just as content as he had been to see Dagur locked up for daring to suggest they should. So now they all wanted to make it up to him by bringing down Viggo once and for all.

When Heather told them her brother's last bit of advice, they were all eager to get started. As they all sat around the table after dinner listening to Dagur's final instructions, Hiccup forced himself to push his guilt and grief aside, saving it for after they hit Viggo's next dragon auction. It was time to concentrate on a new mission, and this time, they'd do it right.

"Yeah!" Snotlout jumped up from his seat and pumped his arms once everyone had agreed on their next course of action. "Viggo, you're going down!"

"This isn't about Viggo," Hiccup said icily, putting down his cup and resting his arm on the table. All this had happened because he'd let himself focus too much on beating Viggo. Whenever he started viewing things from that angle again would be when more trouble started. For now, at least, he was able to stop the man from taking over his thoughts. To prevent himself and the others from focusing on the wrong object, he said, "This is for Dagur."

Heather, who was sitting beside him, covered his hand with her own. "For Dagur," she repeated softly but firmly.

From his other side, Astrid reached over and did the same. "For Dagur." So it went around the table until, one by one, they each promised to avenge the warrior they now all knew was a true friend.