People change for each other all the time. Take any love story, any great love story at all, and you'll see that people have to be willing to change if they're going to make things work out. Like Shrek, when Fiona tells Shrek that she's sick of his burping and farting and everything. And Shrek's like, 'I'm an ogre. Deal with it.' And Fiona says, 'What if I can't?' So Shrek takes that potion that turns him into a hunky prince. He does it out of love for Fiona.