Which tool has not greatly reduced the number of people who have died from infectious diseases?
disinfectants
antiseptics
analgesics
antibiotics

Anxiety, stress, or something like that

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)