How (and when) do you decide that your time is better spent elsewhere? Basically the Silicon Valley catchphrase, "Fail fast" I know that if I decided to spend

How (and when) do you decide that your time is better spent elsewhere? Basically the Silicon Valley catchphrase, "Fail fast" I know that if I decided to spend my next two (or three or ten) years learning Discrete Mathematics I would probably get somewhere. But what if I gave up once I realized that I have more of a talent somewhere else and followed that subject? That aside, I find references to historical successes kind of a truism. Sure, Amazon is successful and Jeff Bezos perservered. It doesn't mean everyone who perseveres at their craft is going to be as successful as him.