To be successful in science, as in most other professions, requires a combination of direct skills (ability, knowledge, industriousness, perseverance, etc.), in

To be successful in science, as in most other professions, requires a combination of direct skills (ability, knowledge, industriousness, perseverance, etc.), indirect skills (e.g. connections, political ability, salesmanship) and luck. As a field gets more overcrowded, the job itself becomes less attractive (lower pay, more hours, less interesting work) and the relative importance of the indirect skills and luck becomes much greater, leading to a lower average quality of practitioners. Presumably, the demand to enter the profession should subsequently decrease and eventually lead to some sort of equilibrium.