Wikipedia says this about diminishing returns:

The law of diminishing returns states that in all productive processes, adding more of one factor of production, while holding all others constant (“ceteris paribus“), will at some point yield lower incremental per-unit returns


For example, that first bite of chocolate cake is delicious and so are the next couple, but a some point the pleasure we receive from each bite diminishes.  In extreme cases we may even eat until we feel sick.

The law of diminishing returns is commonly taught in economics classes but is applicable to all phases of life, such as:

Fitness: at a point working out longer or with more intensity will not get you better results

Nutrition/Culinary Arts: that first bite of a filet mignon, bone-in rib eye, patte, etc brings great pleasure and should be enjoyed ,but at a point the pleasure starts to drop off.  Another example is today’s foodie craze.  Eating nutritious,  organic, expertly prepared local foods is great but when considering time, cost and convenience there is a point of diminishing returns.  We must not look at this in a vacuum without also considering the unintended consequences.  Over time, this will lead to a more desirable outcome.

Rest/Relaxation: we all need rest and “chill” time, I would even argue that in today’s lifestyle many people do not get enough, however there is a point of diminishing returns were one has rested enough and any further rest will lead to undesired results

In the examples above the point at which the law of diminishing returns occurs is specific for each individual.  Only you will know what is best for you and when you are achieving the desired result.  What’s important is to be aware of diminishing returns and to know oneself enough to recognize it.  Maybe the Greeks were onto something, moderation in all things.