Perhaps they suspect you have mental illness and are scared of you or something....if it happens often, this is what I suspect is happening but of course I don't know for sure. I used to accept everyone who friended me and it landed me in enormous trouble so I respect a persons wishes to block people now. I don't tend to like the kind of people who block people for no reason and think it's a controlling power trippy thing to do too, but at least they are smart enough to avoid the mistakes I made so I really shouldn't judge. I like people who are very kind, open and warm hearted as a rule but these kind of people get trampled on so we don't get to see them much....they are probably at home hiding in their closets.