Law of Diminishing Returns
In economic classes, you often hear of the Law of Diminishing Returns, which states that if one input in the production of a commodity is increased while all other inputs are held fixed, a point will eventually be reached at which additions of the input yield progressively smaller, or diminishing, increases in output. If I haven't bored you to death yet, this simply means that there is a point where if more stimulus is added, you get less results. Even though this is an economic law, it applies 100% to athletics. There is a sweet spot of training stress for every individual athlete and it is only through listening, observing, and trial and error that this sweet spot is found. Every athlete's sweet spot looks completely different and is dependent on their athletic needs, family, and work stress.