1.Play this game.
2.Try to do your best.
3.Seeing worse people than you kill the enemy (because they have more luck than cells in there body).
4.Your opponent will always kill you no matter how you move or what you do, but your allies will never hit.
5.Practice aiming 10 hours a day, but it won't help because an opponent with only A and D on his keyboard will shoot you in the head with a P90.
6.Seeing opponents who only play awp because it kills on hit and they can't play with other weapons.
7.Drop to silver rang.
8.Meet the smurf in the match.
9.Timing in which opponents lean.
10.Toxic players or those without headphones and those who don't know what a team is.

You only need to experience one of these steps to get depressed playing CS:GO, but I wrote different causes.
Greetings.
Alansel