What is the problem?

I have one friend, that I used to warned her not to do it. She says that its okay don't worry, and then things just happen as how i warned her.

Is it my fault that i failed as a friend?

or is it a human nature that not listening to someone else except themselves?
why human being always being so over-confident?
is it good that always being so over confident and do not like to listen to others?
haih.