Copy-left invites creative people.
Creative people...
Are easily bored, are willing to take risks, don’t like rules, ask “What if?”, make lots of mistakes, collaborate, are generous, are independent, experiment, motivate themselves and work hard.
Are you creative?

Copy-Left in short means that users can work with the copy-left material, modify it, share it, but under the legal agreement that any modified version is kept free.

Here is a video that expands on the subject.

This is a more artistic way of expressing CopyLeft vs CopyRight