In fact, it is easy to understand why interest in life is lost. People begin to close themselves off from the outside world, do not want to see and hear everything that happens. In a similar way, a person exhibits a defensive reaction that helps to hide from the pain encountered on his life path.
Everyone can remember how often he says such phrases: I do not want to see this, I do not want to hear this, I have no desire to experience this again. During the pronunciation of such phrases, people trigger certain mechanisms:

Destruction program.
Completely close any feelings.
The real world in all its manifestations is no longer perceived.

Regardless of whether a person understands that with such thoughts he gives an order to launch a program of destruction, he acts. A person has several channels of perception, on which the understanding of the surrounding reality depends. How to regain interest in life? You need to learn how to properly perceive the world around you.
If you lose interest in life, what to do? There are some rules for those who have lost interest in life, they will help to regain it.

You need to completely change your schedule. This may be a change in the route that a person follows to work. Perhaps you should abandon the transport that he follows, or get off a little earlier than your stop and continue on foot. Many people find it helpful to listen to their favorite music while traveling and commuting to work. This helps to strengthen the nervous system.

How to regain interest in life? Psychologist's advice: you need to start experimenting and stop being afraid of the new in your life. It is also important to stop eating the same food. Change your hairstyle, if it has not changed for a long time, update your wardrobe. You need to start enjoying all sorts of innovations.
It would be useful to update the interior in your home, you may even have to throw away some old things and purchase new ones. It also helps to add new colors to the interior of the apartment.
You will need to become a little selfish and get rid of those duties that were habitual and took a lot of time, but were not necessary. You need to start loving yourself and stop listening to someone, learn to believe in yourself. Rejoice in any small positive events in your life.