Have you ever tripped over your cat?

I'm always very careful about watching my cats, but they have a way of fluttering about. One second here, and in another they are out of sight. They are truly amazing creatures of stealth. But anyway, sometimes I'm a little careless and don't notice that one of my cats is right at my feet. I start to move and... Once I stepped on my cats tail and she yowled and I felt so terrible afterwards. I'm lucky she forgave me. I read in a book about someone who did that once and afterwards his cat became very aggressive towards him. Today while I was opening the door to come inside, I didn't see my cat waiting on the other side. As I came in she came charging out at the same time, and I kicked her pretty hard :( I feel so guilty. She looks to be ok. She meowed sadly afterwards, but I pet her and gave her some treats, and she looks to be ok and was purring. Am I the only one that is this clumsy? Each time it happens I always promise myself to be more careful.