Where do your best ideas come from?

Some of my best ideas have come to me from other people!  Yes I hear what someone is talking about and bam!  I have an idea based on what information someone else has told me or what I have read.  I am not shy about admitting that I get a lot of good ideas from other folks.  I add some fertilizer, water and nurture and I have something that turns out to work quite well.
I am not afraid to say thanks or give credit, I find in most cases the people who give me the seeds I start with are quite surprised that I have turned what they said or wrote into a productive idea.  However they are always happy that they shared something with me that clicked.
So why do some folks just refuse to accept anther's idea because they feel it has to come from inside themselves to be any good?
This puzzles me when someone will flat out reject a colleagues ideas just due to ego.  Or is it something else.  I see things in a different way.  If a business or venture gets some help from someone outside the ownership or artist, and that help moves it ahead even a little bit, who cares who's idea it was?   Success finds its way to the venture or business that is open to the universe.  I would rather get 100 ideas from other people and prosper than come up with one on my own and flounder.