When producing something, there are inputs and results. The law of diminishing returns states that simply increasing one input but keeping others the same will at some point yield diminishing results. In some cases, this can be improved by adjusting other inputs appropriately. For example, if adding more workers to a factory, we can also add more machines and working space. In other cases, the production may be inherently difficult to parallelize.
Brook’s law states that just increasing headcount in a software project, will not make it ship faster. Ramp-up time, communication overhead, and the indivisibility of certain tasks may in fact slow it down.
In our personal lives, we may find that doing too much of something may lead to diminishing (or even negative) returns. For instance, over editing a piece of writing or continuing to tweak a painting.