Saving a penny has a higher return-on-investment than attempting to earn an extra penny.
It is, on average, easier to do (since you’ve already earned the money). And, thanks to taxes, you’ll have to earn more than a penny to have that penny in hand.
This logic works for happiness too.
If happiness is reality relative to expectations, an expectation lowered has a much higher return-on-investment than a corresponding improvement in reality.
Aside from being undoubtedly easier to do, it has the added benefit of freeing us from the fear that prevents us from taking the kind of action that can actually step-change our reality in the long run.