“Repeated complaining rewires your brain to make future complaining more likely. Over time, you find it’s easier to be negative than to be positive, regardless of what’s happening around you. Complaining becomes your default behavior, which changes how people perceive you.”
The more you complain, the more you will find to complain about.
If you feel the need to complain about something, he suggests you complain with a purpose, be specific, and start and end on a positive.