Any psychology text book will tell you that each of us has a well-defined self-image that we can describe in detail, and that we have a driving need to behave consistently with our self-image. Your self-image determines how you see the world, how you react to your environment, how you define the things you feel you need to do, and how successful you are when you attempt to do them. It is virtually impossible to behave inconsistently with your self-image. If you see yourself as a smoker, you will find it near on impossible to stop smoking. If you see yourself as overweight, you will find it nearly impossible to reduce your weight. Likewise, if you see yourself as underweight, you will find it nearly impossible to increase your weight. Trying to behave differently from your self-image is nearly impossible.
It is also highly likely you have personal experience of someone you know who suddenly changed their personality. Maybe they were very timid and suddenly became assertive. Maybe they were highly motivated and suddenly lost interest. Maybe they were exceptionally lazy and suddenly became massively energetic. This sort of radical change often happens just after a highly charged emotional event. Perhaps an accident, a death, a violation, or perhaps an exceptionally embarrassing event.
Regardless of the situation, the thing that has changed is the person’s self-image. Maybe a timid person is thrown into a situation they must do something brave. They do it, and immediately their self-image changes. They now see themselves as the person that did that brave act. They suddenly felt empowered, they acted, and immediately their self-image changed. It can happen in the other direction also. A confident person experiences failure and immediately change their self-image. They then find it hard to continue to act confidently in other situations.
This sudden change in self-image happens many times every day to people in all walks of life. It is so common that there are many books and courses designed to help people deal with the negative consequences of unwanted change. People that make positive changes just enjoy the benefits and move on with their lives. You can make these changes to yourself without needing to experience an external disaster. There are many good books, courses, and counselors that can guide you through the process if you have trouble doing it on your own.
The first thing to do when you go vegan is to start seeing yourself as a vegan. Create a new self-image in which you are the vegan you want to be. Imagine yourself in situations where you are a vegan behaving in a normal vegan manner. Imagine yourself with the ideal body type that you want. The one that goes with living a healthy vegan lifestyle.
See yourself as a vegan rather than a person that is trying to go vegan.