Knowing when to quit is difficult. Fortunately, there is science and math to help us, as this article in plus.maths.org explains:
Knowing when to quit is one of life’s great dilemmas, whether to persist in the face of diminishing rewards, or to quit now in the hope of finding richer rewards further afield. For every gold mine, eventually there comes a point when the amount of gold extracted can no longer justify the cost of keeping the mine open; once that point has been reached, it is time to quit, and start looking for a new mine.
Similarly, for a bird feeding on caterpillars in a bush, there comes a point when the calories gained can no longer justify the energy expended in searching for more caterpillars; once that point has been reached, it is time to quit, and move to another bush. And, for a honeybee, there comes a time when the weight of pollen collected can no longer justify the energy required to carry that pollen; at that point it is time to quit collecting, and fly back to the hive.
Fortunately, there is a mathematical recipe, embodied in the marginal value theorem (developed by the American ecologist Eric Charnov in 1976), which specifies when to quit in order to maximise rewards. More importantly, the marginal value theorem has an enormously wide range of applications, from its origins in optimal foraging theory to how brains process information. In essence, the marginal value theorem provides a general strategy for maximising the bang per buck, irrespective of the nature of the bang and the buck under consideration.
Wait you say: it’s Friday afternoon! You know when to quit (at least for this week). Ok, that works too. But if you need more general guidance, read the article.