When spotting a dead lift, it is important to
a - move up and down as the lifter moves.
b - keep your hands on the bar at all times.
c - remember not to touch the lifter unless needed.
d - stay stay away from the lifters so they don't fall on you.

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)