What forces work to make people feel bad about their body image

The main forces are social perception and attitude of others.

Explanation:

The current model of a perfect body is one that is thin and fit. This image is shown on advertisements, movie and TV stars, and most viral videos.

The current fad has not always been the case. For much of history, and in other cultures right now, more shapely curves are thought of as normal and desirable. Even today, there is a range of what people like and do not like in terms of the shape of a body.

A person that does not fit this image may feel bad about their own body, unless they develop courage to just be themselves. They can decide that the are OK as they are, and that the opinion of others just does not matter. They can decide that how a person acts, behaves, and cares about others is more important. Then they can overcome negative feelings based on the opinions of others.