Why is it important to consider social life when making a diet plan for an individual

Because you don’t want to go on a diet and then go out with your friends because you’ll be influenced to drink/break your diet.

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)