The main reasons people complain are:
To Get Attention: The primary need people have is to connect with others. A person may complain to a stranger about the weather or a local sports team as a means of starting a conversation.
To Avoiding taking action: People will complain to avoid trying to improve society and themselves. When someone says, “Everyone in my family is overweight” it excuses them from adopting a healthy lifestyle.
People also complain to avoid social embarrassment. A person who wants to ask someone to a dance may complain that the other person is “stuck on themselves” as a way of excusing themselves from asking and possibly being rejected.
To Pre-excuse poor performance: A person about to sing before a group may complain that they have a scratchy throat prior to performing to lower expectations should they not sing well And someone about to take an important test may complain that they didn’t get enough sleep to reduce embarrassment should they not earn a good grade.
To Brag: A complaint may be a cry of superiority. It implies that the complainer feels they don’t have whatever fault they are complaining about. People will also complain about poor quality as a means of letting others know that they have high or refined standards. A person may complain about the food or service at a restaurant as a way of letting all who hear know that their disapproval of what’s being presented proves they are arbiters of quality.
To Exercise Control: In "The Seat of the Soul," best-selling author Gary Zukav wrote, "complaining is a form of manipulation." People often complain as a means of inciting others to abandon an alliance and switch to their point of view. Complaining is used to build support and power by focusing on what is wrong with another’s position. Complaining is used to lobby for a majority position of control.
-Paraphrased from "A Complaint Free World" by Will Bowen | 
