Who you are is the product of all of the experiences you have had, and not had, throughout your lifetime. Nobody operates in complete isolation. Everyone is influenced by sources outside of themselves. We take those experiences and internalize them with our other memories in our own way but ultimately everything you come in contact with serves as material for the future you. So it stands to reason that new ideas & creativity are also the result of taking existing ideas and transforming them.
People frequently talk about ideas/people as being "totally original," but the truth is that originality is rather unoriginal. People with seemingly totally new ideas are really just the result of taking existing concepts and bringing them together in new ways. Perhaps you can identify the original source material, perhaps you can not, but everyone is influenced by ideas outside of themselves and nobody creates something entirely new.
The 4 part video series Everything is a Remix is a fantastic exploration of this in action. From music, to film, to mechanical invention everyone is influenced by the work of others.