Oscar (Michael B. Jordan) and his girlfriend (Melonie Diaz) on his last day.

“Fruitvale Station,” out Friday, is an extraordinary film for a number of reasons, and many of them are small. There are big things right with the fact-based film — particularly the performances of Michael B. Jordan as Oscar Grant and Octavia Spencer as his mother.

The magic of movies, though, lies in the little things, and “Fruitvale Station” is full of small moments that pack a big wallop. And in one of them, I saw myself.

Early in the film, Oscar goes to a grocery store to pick up supplies for his mother’s birthday party. Standing next to him is a woman struggling with the ingredients for a fish fry. Oscar turns to her and asks if she needs help. And she takes a step away from him. He’s black. She’s white. She’s me.

Look, I can bust out the some-of-my-friends-are … trope as well as anyone. I spent a year teaching in a high school on the West Side of Chicago where every student was African-American, and I spent the rest of my teaching career in a school that had no ethnic majority. I’d like to think I don’t have a racist bone in my body. And yet I understood that step she took, that synapse that fired in her brain to warn her that the young black man next to her, trying to help, might be a threat. Let me be clear: I’m not saying it’s right. I’m saying I understood it.

When “The Help” came out in 2011, I wrote a column about how Emma Stone’s character, Skeeter, was unrealistically aware of her white privilege. “The Help” made tons of money, partially because it made white filmgoers feel good about their place in a society where racism still exists; I wrote that most white people today were sure they’d be Skeeter, the Great White Hope, and not any of the film’s more hateful white characters.

“Fruitvale” does the opposite; there will be plenty of white women who will see themselves in that step. And they’ll feel ashamed. And maybe they’ll feel that way again each time a young black man gets on their elevator and they shift their weight just a bit.