I am an Ivy League-educated professional who regularly has to write for my job, who was always in the top English classes in school. And sometimes, I mix up “your” and “you’re.”
I know how grammar works. I always, if I stop to think about it, can figure out which one to use. I know all the tricks. Most of the time, I don’t have to think about it, and the right one comes out. But sometimes, I’m just thinking in terms of what sounds I would make if I were speaking, and I’m in a rush or just distracted or just glitching, and the wrong one comes out.