Switching:

David Epstein:

"The important trick, he said, is staying attuned to whether switching is simply a failure of perseverance, or astute recognition that better matches are available."

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Also see:

Randolph M. Nesse, Good Reasons for Bad Feelings:

"If you ever spent an afternoon picking wild raspberries, you have experienced the emotional changes that guide foraging. Finding a bush laden with ripe fruit arouses a tiny thrill. With joyful enthusiasm, you pull off berries in handfuls, some of which are so delectable they never make it to the bucket, As the bush gets depleted, the berries come more slowly, then slower yet. Enthusiasm wanes. Finally, you are reaching through prickles to try to get that one last deformed berry. Your motivation for picking from this bush is gone, and a good thing, too. It is senseless to try to get every berry from every bush. However, jumping too quickly from bush to bush is also unwise. How long should you stay at each bush to get the most berries per hour? The problem may seem abstract, but making such decisions well is crucial to the fitness of nearly every animal.

The mathematical behavioral ecologist Eric Charnov came up with an elegant solution, one that illuminates much about mood in everyday life. To keep things simple, assume that it always takes the same amount of time to find a new bush. ... When you find a bush, berries come fast at first, then slower and slower yet; ... The longer you stay, the more berries you get from that bush, but to get the most berries per hour, you need to stop and go looking for the next bush at just the right time.

The best time to stop is at the point that gets you the most berries per hour ...

Charnov called this the Marginal Value Theorem, because all the action is at that spot "on the margin" where the rate of getting berries at the current bush dips below the number of berries you can get per hour by moving to a new bush. The core idea is simple but profound. You don't have to do calculus to get the right answer, you just need to follow your emotions. To maximize the number of berries you get in a day, go looking for a new bush whenever you loose interest in the current bush. Thanks to your emotions having been programmed by natural selection, that will generally be the point at which the rate of berries coming from the current bush slows to the average number per minute across many bushes. This decision-making mechanism is built into the brains of nearly every organism. Ladybird beetles, honeybees, lizards, chipmunks, chimpanzees, and humans all make such foraging decisions well. No calculation is needed; motivation flags at the optimal time to make a switch.

The decision about when it is best to quit one kind of activity and do something different follows the same principle."