Nothing we will ever do in our lives is formed out of complete originality. From birth we are taught things that have been taught before. Society’s very existence depends on duplications of language and belief. It is our own ignorance that makes us think we are original.
However, I would say that we do not “steal” original thoughts because we mean to be vindictive or claim other’s ideas as our own. In a way it isn’t our fault, but yet also entirely our fault.
Pure originality is the inability to pinpoint the particular sources from which something was created.