Have you ever done something wrong without knowing it?

I was walking in Manhattan and saw this brand new book on a bench. I took it without thinking, without stopping. But I started wondering about the provenance of this book and remembered a guy standing next to the bench with his cell in his hand and a cigarette in the other. So I figured I had stolen a newly bought book put down by a busy guy.

This is an innocent and trivial example, but have you ever done something wrong and realized it was wrong only later, when the harm was already done?