John didn't realize his blunder until it hit him in the face. Luring one of the Fair Folk into a trap was fraught with risk, but John was too stubborn to listen to Bobby or Jim when they warned against fighting a Fairy in her own element. The mistake wasn't setting the trap; the mistake was using Dean as the bait. John should have known that Dean's trespass wouldn't entice the rogue Fae to move in for the kill; his fair face would tempt her to possess him as her own.
The storm raged around John, as wild and uncontrolled as the creature he faced. She was incensed at being summoned and infuriated at being denied. Later - much later - John would come to understand that it was nothing he had done that had resulted in saving Dean. The storm, the tide, the elements themselves seemed to conspire against the mad Fairy; she lost her focus, lost control and was consumed by the very power she sought to wield.
John staggered to his feet and fought against the wind to make his way down to the shore. Dean, free from the Fae's compulsion struggled against the water and the tide toward the beach, but was caught in the tentacle-like seaweed the Fae had summoned to ensnare him. Weakened by the poisons it had injected into his body Dean fell face first into the surf and was unable to prevent himself from going under.
Screaming Dean's name John leapt into the crashing waves. The seaweed seemed sentient and determined to drag Dean his death even without the Fairy's directive. John slashed and hacked at the bonds with his steel knife even as he fought to pull Dean far enough out of the surf so he could breathe air and not salt water.
Slowly, slowly John waged his battle against the sea until it finally spat him up on the shore clutching Dean against his chest like a hard-won treasure. He tried to crawl higher to put them out of the reach of the relentless waves, but his strength was gone; the water that lapped at their legs and feet mocked John's inability to truly escape.
The poison that had slowed Dean's limbs, had limited his breathing as well. Dean convulsed and twitched weakly in John's arms. In those moments John couldn't even look at his son's face; Dean's body was fading but his consciousness was not. He even spoke before John did whispering, "I'm sorry, Dad."
John sat stunned on the beach unconsciously rocking Dean like he had when he was a baby. In his head John whispered, shouted, said aloud all the things Dean needed to hear. Mostly, John apologized for the life he forced his son to live, the risks he made him take, the chances he never got to have The tears that fell down his cheeks mixed with the salt water slowly crusting on his face; who would ever know the difference between the brine of Mother's sea and a salt of a father's tears?