You are right, you do not need something to happen to you before you start being careful.
However, as long as this part of the conversation is about my safety, I am very careful. Coming home by 11/12, once or twice a week, when the bus drops me literally minute and a half away, cuts down my chances considerably. My bus is a busy one and I see more weird people on the subway, than I do on my bus.
Again, not taking my safety for granted here, but I need not be paranoid either.