Just as your eyes are for seeing and your heart is for pumping blood, your mind is for solving problems.
To do this, it stores information, sifts through possibilities and generates solutions.
However, without anything else to occupy your thoughts, your mind will generate its own problems and start trying to solve them.
This means that in the absence of other stimuli, your mind is inclined to drift to negative situations and interactions — problems in other words
Unfortunately, the solutions most of us habitually generate are highly critical of ourselves or others.
The obvious way to avoid negative rumination and self-criticism is to give your mind a more constructive problem to think about.
Here is one: How can I make my life and the lives of my loved ones more pleasant?
(From my book 52 Secrets of Psychology).