There'd really be something hugely wrong if a book that is basically a dude telling his own story didn't have him as the guy we are all rooting for. Tevye is our main man here. We want him to do well, we want his plans and schemes to succeed, we want him to get a second chance with his bad decisions, and we really want his enemies to just stop being so freaking mean to him already. And all that? That's how you know that he is the protagonist of the story.