“A compelling protagonist is one who feels like a real person to the reader; it's as simple (and as difficult) as that.” - Layla AlAmmar, author of the novel Silence is a Sense.
Protagonists are just like you and me.
John Mclane in Die Hard is just a policeman on his way to visit his estranged wife and their kids on Christmas eve. Before the chaos unfolds we see his struggle; to keep his wife, to see his children, to have possibly his last Christmas with them as a family. We already like him before he starts fighting the bad guys and saving the day.
That's what a good protagonist looks like.
They are usually flawed in some way, just like us, and their struggle to make it through the story that unfolds is what makes them relatable. But it's not quite as simple as just making them the same as us; they have to save the day in a way that's not too easy, their character has to act and react in a way that still makes us like them at the end.
Batman never kills the baddies. That's his thing. He could be completely unrelatable; he is a billionaire with all the tech and gadgets, after all. Not many of us have a mansion and all-singing-all dancing car. But he has a heart. And we love him for it.
We may not always agree with the actions our beloved protagonists take, but we must want them to succeed, because there's something about them that we like. It is their actions that drive the story after all, their problems that need to be solved.
John Mclane had to act because his wife was being held hostage. If she wasn't there, he might still have saved the day, but he would have had nothing to lose. He did it all for her, and we all like to believe we would fight off terrorists and Hans Gruber for the ones we love, so we relate to him more.
Our protagonists know what they want, and they drive the story from beginning to end just to get it, stopping at nothing to achieve their goal. I don't know about you, but I think I definitely need to be a bit more of a protagonist!