Complaining too much can cause too many health related issues in daily life such as heart attacks and sleep disturbances. Or harder to do task at work school or daily living it might be difficult to relate and make friends with people if you complain too often to them because it can be selfish
In my opinion, people who complain a lot are likely to have more health problems than someone who is content in any circumstance. If someone is always complaining, it is a sign that they are unhappy, not content in their life, and possibly even that they worry too much. All of these things add up and the result can be depression, anxiety, and dissatisfaction with their life.
Everyday people complain about the smallest things that really don't matter. There are many reasons people complain. Some people complain about homework, or bills, or gas money for their car. Complaining and worrying about all of these little things is not good for your health. Everyday doesn't have to have a smile.
Complaining can be a useful way to externalize issues that may be causing discomfort internally. Keeping bothersome issues bottled up inside cannot be healthy either! Complaining can be a way for someone to process information and resolve their own issues by talking about how they feel about things out loud.
Being aware of yourself and your health situation means taking an active ownership of your body and your personal well-being. People who are more in tune with their personal situation are more likely to discover actual problems before they become critical and potentially life-threatening, which both helps themselves and saves taxpayer dollars.