Well, due to my depression, i have read lots of philosophy and ideas on life.
Basically everything in life has an opposite, positive/negative, dark/light, night day, good/bad, north/south, left/right etc ect
without one there can not be the other,its impossible, without having a reference point from bad you cant have good, this is a universal law found in nature, everything has its season, spring/summer/autumn/winter, life, death etc
the opposite of depression is expression, when you are depressed you are literally depressing emotions, bottling up and going inside yourself. that is why exercise helps, movement of the body, shaking, vibrating, yelling, screaming are all outlets of expression.
Anyway it is true the harder you get hit the better you get at dealing with hits, it develops a weird determination that cannot be built any other way, its do or die, fight or flight. discomfort is literally training you to deal with discomfort you are practicing being uncomfortable, view each obstacle in your path to grow, let pain be your friend it is helping you to grow. we go to the gym and go thru pain to grow our muscles.
One cannot know true pleasure without knowing pain, pray for challenges guys

Couple of my fav you tube guys are...
Eric Thomas for motivation
https://www.youtube.com/watch?v=zJHo6DsJJMsElliot Hulse for philosophy/thebody/emotion n thoughts
https://www.youtube.com/watch?v=M4Ko32D5ALw