I suspect that in many competitive fields persistence actually hurts people in aggregate, and everyone would benefit if everyone agreed to be less persistent. For example, in a sports competition with a large prize for #1, making people more persistent won't grow the size of the prize. After a certain point, the sum of resources spent by all participants will be greater than the prize, but by the deadly logic of game theory, everyone will just keep spending more and more. The same thing seems to be happening in music/art/writing/acting (because popularity is a zero-sum contest), and parts of the startup scene (for the same reason).
One good trick is using the "outside view", deliberately tricking your brain into ignoring all the special details of your situation and looking at the typical case instead. For example, "how long do you think your classmates will take to finish their theses?" vs "how long do you think it'll take you to finish your thesis?" Studies show that asking the first question yields a much more accurate answer to the second question than asking the second question directly :-)
I try to come up with some objective metric. "I think I'm fast, how does my 50 yard dash compare?" "I think I'm smart, how were my grades? And standardized test scores?" Even still, the smartest amongst us have the best ability to lie to ourselves. Everyone thinks they're in the top half, and most in the top quartile.
Then you can try to adjust the starting conditions, and ask what happens to the typical person who decides to do gamedev while having a day job. The answer is again obvious, they stay afloat financially but fail to complete the game.
And so on, you keep adjusting the starting conditions until you find a scenario that works for the typical person. This is similar to the startup advice saying "make a product that people would buy even if it wasn't very good".