I finally watched Dune 1 and 2, and I have some thoughts that are probably controversial. But in the movie, I watched, Paul didn't have a choice. If he hadn't become the messiah, the Baron and Feyd would have wiped out the Fremen. The Baron literally said in the first movie to kill them all, and I think we all know Feyd would've killed them all! Not to mention, Jessica has literally been manipulating and grooming Paul his entire life. She planted the idea that he needed to drink the water of life, and she orchestrated all of that. Paul makes it clear he doesn't want to go south because he knows if he goes south, he will not be able to escape the path laid out for him. Chani's the one who convinces him to go, and I don't think it's fair of her to blame him when he clearly didn't have a choice. He drank the water of life because he was trying to see how to save her and her planet. He's seen glimpses of a terrible future, and he's trying to prevent it. The thing is we have no idea what Paul saw when he drank the water of life. He says he saw so many possible futures where they failed, but there's one way for them to succeed. After he drinks the water of life, after he sees these possible futures, his personality changes drastically. He fully accepts the role of the messiah, and he even sacrifices his own happiness. But why? I think it's because he's seen something about Chani. I don't know what, and I'm not sure if we'll ever get to know. But whatever it is, it's enough for him to do whatever it takes to protect her, even if he loses her in the process.