People complain for a wide complexity of reasons; some of those could be ~
Emotional regulation ~ Sometimes people complain as a way to manage their emotions. By “venting” their feelings, they hope to lessen the severity of these distressing sensations.
Mood ~ People may be more likely to complain when they are experiencing negative moods. The problem with this is that people complain more when they are in a bad mood, and their constant complaining then leads to further negative moods, creating a vicious perpetual cycle.
Personality ~ Research suggests that certain personality traits play a role in how frequently people complain. Perhaps not surprisingly, people who rate high on the trait called agreeableness are the least likely to complain.
Social factors ~ Other people can also influence how often people complain. Being around people who tend to complain a lot can make people more likely to air their own grievances. Shared complaining can also serve as a form of social bonding as a reminent of our ancient history of civilization building.
Complaining can be useful at times, particularly when it is done mindfully in order to address a problem. By limiting your complaining and using it to advocate for yourself, you can make sure that it serves a purpose rather than dragging you under.