Mastery is where the marginal returns flatten out
To become a master of a skill, you have to go way past the point of diminishing returns:
Now the problem with that is that there is nothing more kryptonitic to a person’s Fighting Spirit, and to winning, than comfort. Nobody ever got anything done by being comfortable. If you are not working hard, you are not learning; if you never get past that point when a new project becomes actually difficult, where the marginal returns flatten out, then you will never be a master. Everything worthwhile is going to hurt, and if you avoid pain, you will fail. Etc.
And this summarizes why self-reported happiness is a worthless statistic:
Thoreau said that most men lead lives of quiet desperation. It seems that that’s true, but with the following proviso: some men do eke out contentment, and they get there by gradually ratcheting down their expectations. Their appetites fade. They compromise, and rationalize, and eventually settle.