One exercise myth would be- if you do a lot of crunches you will have "six pack" abs. This is incorrect because if you have fat on your stomach, the crunches will create muscle not burn fat.
Another exercise myth- muscles turn to fat when you stop exercising. This myth is not plausible because muscles are almost impossible to go away. Your muscles have muscle memory which makes it extra hard to "forget"!
Last exercise myth- strength training makes women muscular and unfeminine. This is not possible because strength training tests your endurance not how much you can lift. However, lifting weights would give you muscles! <3
Low self image could be caused by bullying, just overall not liking yourself or other things. Low self-image can cause depression, anxiety, eating disorders and other things that are harmful to you and your body.
The things that most strongly influence your personality are your environment, your genes, and your experiences. It has been shown in studies that the environment and our genes both play an important role in determining what oulr personality would look like. However, what we experience personally also affects how we will behave and what kind of personality we will have. For that reason it's a combination of the three.