People who complain about everything avoid taking responsibility for their lives, and it's easy to have a long list of excuses why they aren't reaching their goals. Without knowing it, they're focusing energy and attention on things they don't want and probably fail to realize how much they are complaining. It's a sad sight to witness when people give their power away and at the same time use complaining as a form of control.
Persistent complainers show they aren't focused or skilled at time management. They could also hold a grudge. If there is too much work to do it's the boss's fault. If they didn't get to work on time it's the fault of public transportation. If they got shafted for a promotion there must be a conspiracy at work. It doesn't matter what their circumstances are. Somebody is out to get them and if there is another person nearby who listens with a sympathetic ear the complainer's issues are validated. Is that all they want, to be heard?
That could be it. But, the difference between the complainer and the one who takes action is that the complainer has given up on life. A successful person is the one who complains and then figures out what to change to achieve the desired result. Complainers succumb to defeat right to the bitter end. They lack the perspective to see the next step and expect everyone else to drop whatever they're doing to come to the rescue.
Complainers use their rants to spark conversations. There surely is in human nature an inherent propensity to seek out others who share the same types of thinking. Complainers utter their displeasure to create the illusion of superiority because others don't adhere to their standards, and to get the listener to switch allegiances. That's the reason why somebody who was otherwise satisfied with life can get stuck on a downward spiral of complaining. It starts off with one or two people complaining about their lives, and after some introspection others will think their own lives aren't so great. Before anyone knows it there's a competition to see who has it the worst.
Perhaps this attitude started early in life and was carried right up to adulthood. Stemming from abuse or lack of attention at home or at school, complainers haven't learned to love themselves. Therefore, it's the job of everyone else to listen and to give the support the complainer never had. That won't work. Friends will disappear one by one and complainers will lose their audiences.