Sanzo is a liar. One might expect that a priest ought to be religious, but Sanzo isn't. Not in the conventional sense, at least. Sanzo has his own brand of religion. It's very zen, and very hard to understand, and very hypocritical. But Sanzo stands by it, and he couldn't give a fuck if you dimwits can't wrap your stupid primate brains around the philosophy, so fuck you.
In Sanzo's religion, smoking, drinking, and killing are allowed. And so is lying.
Most of the time, Sanzo prefers to keep quiet rather than make up elaborate falsehoods. When he lies, it's in his actions and his thoughts, and in the way he treats his companions. He says he'll kill them, but he never does. When Goku tries to hug him, Sanzo gives him the cold shoulder and a whack on the head, and then he tells himself that he hates them all, but he doesn't.
In the moments where he is forced to admit that what he feels isn't just hatred and annoyance, Sanzo tells himself that they don't mean enough for him to expend the energy to hate. They mean nothing to him. He is free; he is bound by nothing. He will live his life as a paper airplane – alone and unfettered.
He is certainly not a kite. They are certainly not his string, allowing him to fly higher than any paper airplane could ever hope to go. That's just ridiculous.
Gojyo is a liar. Hey, it comes with the package, and what a nice package it is! Rawr! Gojyo is a great gambler, and poker is a form of lying. Sweet talkin' the ladies might sometimes stretch the truth just a bit, too, and if Gojyo's got anything, then Gojyo's got that, baby.
For all his hedonism, Gojyo is a very simple man. All he needs to be happy are booze, smokes, and women. Sometimes the booze addles his brain so much that he can't remember her fist in his hair, or her claws slicing through skin. Having a cigarette filling the air with the acrid taste of tobacco takes his mind off the memory of a child's swollen, bruised cheeks, mouth filling with the taste of blood.
And the women! Gojyo thinks he could do without the booze and the smokes if he just had women. They wrap themselves around him, soft and warm. They whisper sweet nothings in his ear and place tickling little smooches on his scars, as if kissing them away. Everything is happy and numb in the pub.
Gojyo tells himself that he's just a wicked man with wicked desires. He just happens to like fucking, okay? This has nothing to do with her.
Hakkai is a liar. Of their little group, Hakkai thinks he is the worst offender for this particular sin. Then again, Hakkai thinks he is the worst for a lot of sins. While the others may lie on occasion, everything about Hakkai is a lie. He lies so much that he is nothing but a mask, and he knows this. He envies Sanzo and Gojyo for their ability to lie to themselves because Hakkai has always been truthful to himself.
Hakkai is a very kind man, but Hakkai isn't real. Gonou is real. Gonou was an angry boy who became an angry man. When he was reunited with Kanan, he thought her purity could cleanse him, but it didn't. Instead, he fucked his sister in every sense of the word. He fucked her. Then he killed her.
And then he killed, and he killed, and he killed. He butchered them all. He sliced into their muscles, their tendons, their bones. He bathed in their blood, the men, the women, the children... He can still hear their screams.
Gonou is evil. Gonou is real.
Hakkai thinks that maybe if he wishes fervently enough, or throws himself more fully into their duty, or believes in Sanzo enough, or trusts in Gojyo enough, or dotes on Goku enough… Maybe he can start to fool himself. Maybe he can bend his lies into reality.
Goku is a liar. Everyone thinks that he's too open and too stupid to be a liar, but Goku knows better. His brain might not be the biggest meat bun on the plate, but his heart is definitely the sweetest mango pudding in the…uh… That is to say, Goku has his own type of wisdom.
He doesn't remember anything about the time he spent in Heaven, but there are things that just can't be forgotten. He might not have the memories, but he has the impressions of emotions. Sometimes one of the others will do something, and Goku will think, "Ah! I've never seen him do that before, but he used to do that all the time!"
Goku knows them, and Goku knows that he knew them from before, in the same vague way that he knew that he knew Sanzo when they first met, and in the same vague way that he knew Sanzo was coming for him before they ever met. Goku knows a lot of things, though he doesn't know how he knows them. Nor does he care.
What's important is that he knows how they lie, and he knows how to cheer them up by pretending not to see through it.