The quickest way to mediocrity or worse (less) is to do what most people do, taking the easy road and the "short cuts" in life that are all too common. In this way they are taking what are called "The path of least resistance" (easy) and also "The expediency factor" (fast and easy).
To quote Brian Tracy "...most people do what is expedient, what is fun and easy rather than what is necessary for success."
Lack of self control and expediency factors which causes is to try to take the quickest and easiest way out not thinking about the long term consequences