Warning: grammar rant. Nothing to see; move along.
I've seen this at least half a dozen times in stories (both submissions and published stories) in the past week: use of the word may in past-tense narrative. Made-up example:
She walked down the street. She decided she may turn left for once, but in the end she turned right, as usual.
Now, I admit that I wasn't formally taught this 'til after college, but I'm pretty sure I understood it intuitively long before that: the past tense of may is might. People get confused about this because might can also be used in the present tense, to indicate less probability than may or more formality. Nonetheless, may is just not the right word if you're writing in the past tense. The situation's analogous to can and its past tense, could; I think most people know better than to write
I wished I can do it, but in my heart I knew I can't.
It's obvious there that could and couldn't are called for. But somehow the dual meaning of might messes people up (that's my theory, anyway) and they think they'd better use may.
Okay, I feel better now.