I guess that if you came up with some completely novel idea, say facetiously, some cyrpto-subscription knock-off of flappy bird where you play against others. I can almost guarantee that if it showed any kind of traction, somebody out there would copy it either directly, or similarly enough. Then, if they get the execution down better than you, that's their start-up company taking off.
It's the whole red ocean/blue ocean analogy - there's more good ideas out there already, badly executed, that are just waiting for you to pick up and do better.