He speaks the truth
Stop caring about your rating and you will be free

True in a sense. I had a 12 game losing streak and my online rating only went down 50 points. Of course, I played in tournaments way over my head. Then I went on a 13-2-2 streak and everything was right with the world.
Pllayiing way over your head makes you a better player perhaps. It definitely teaches you humility.

rating shows you progress, without progress you get mad, that is why you should care. but not during the game, put all the focus on the board.

Of course, if you are thinking at all about ratings during the game, you will be scared to lose. Which will make you play worse or less interesting games.
Using it to assess improvement can be ok if you aren't spending too much time obsessing about it. Set a goal and forget it, IMO. The people who become the best at things are the ones who become immersed in the game itself, not worried about a number rating.
To improve, play, and enjoy chess.
Hard to do, but worth it.
As a bonus, your rating will probably go up quicker.