What does the word repetition mean? -to perform different exercises
-muscles become shorter and tighter
-how much weight you can lift one time
-the number of consecutive times you complete an exercise

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)