Javert, the police inspector who has been pursuing Valjean for years already and will keep doing so for years more before the show is over, sings to Valjean "Men like you will never change." But of course it's Javert who never changes, and when in the end he does change he kills himself immediately because he can't cope with it. (Oops, spoiler, sorry.)
Valjean, on the other hand, sings to Javert "I'm a stronger man by far," yet Javert in his dogged pursuit displays undeniable strength and determination; he is, in his way, even more indefatigable than Valjean, the hero of the story. Javert does, in fact, catch Valjean in the end, and it's only Javert's change of heart that lets Valjean escape. It's Javert who is the stronger man, and after running from him for so long Valjean can't help but know this.
You know how the things we don't like about ourselves are also the things that drive us completely bats when we see them in other people? This is, I think, a technique that we writers can use to tie our protagonist and antagonist together. If each one sees in the other his own flaws magnified and despises him for that, that deepens and strengthens their relationship and makes the climactic confrontation more inevitable and powerful.