the way i understand it is that math-wise we already know how many bitcoins there are overall - mined and in the so called unprocessed-ether out there, awaiting miners to uncover them.
This way, it's hard to assume it's created, if it were created then anybody could generate them and their value would be nil. On the other hand, if there's a fixed number and obtaining it is hard then it's "uncovered" so to speak.
If you want to understand how it works then comparisons with fiat currency -although instinctively made because we're human beings- need to be kept at a minimum at best.