These are 3 of the 4 priniciples of training.
Overload: fitness and/or physical adaptation can only be improved upon by training more than you would otherwise.
Progression: slow and gradual increases to the amount and intensity of training are necessary to effect change
Specificity: the conditions and parameters of training should use and meet those that are required by the specific activity to achieve improvement in the body parts that is necessitated by the task, sport, or activity. "practice like you're going to play"