When a person is not an adult he is a child.

Tautology is circular reasoning.
Tautology has the form of an answer without any substance.
Why did the chicken cross the road?
To get to the other side.
This says nothing and, as any 6yr-old can tell you, is silly.
Why is Suzy depressed?
Because she has a chemical imbalance.
Same situation as the chicken joke. Circular answer.

We already knew the chicken wanted to get to the other side. That's included in crossing a road. A useful answer might be "to get food" or "to fight off an invader" or "to mate". A useful answer is satisfying. A useless answer is either comical or frustrating. In search of an explanation many people accept "chemical imbalance" as an answer as if it is a cause. Many people are not frustrated by the "chemical imbalance" answer and they don't see it as comical. They have accepted it. They accept the tautology.

Tautology is the act of making a circular answer sound useful.
Tautology is culturally accepted for some topics.
Perhaps you are getting the point and can see to the end.
Why is Suzy depressed?
Because she continues to struggle against a lost cause or
is using the wrong method.
Depression is nature's way of telling you that your struggle has, for a long time, been a losing battle.

There are similar answers for anxiety, schizophrenia, manic-depression, and fighting with your spouse.

Why are they fighting?
Because they like arguing.
paleological tautology (5yr-old's answer)

Why are they fighting?
Because they have different opinions and want to communicate how severely each holds the opinion.
teleological tautology (8yr-old's answer)

A useful answer: Stop struggling and start solving.
Why are they fighting?
Because they aren't problem solving.
Understanding psychology is understanding the path from infancy to adulthood.