Because a poor self image can sap the confidence out of a human being. Literally sap the strength out of him/her.
If you have poor self image concerning your physique when you get to the university see if you can find one of the strength coaches. They work with athletes in every sport increasing their strength and stamina. They know how to deal with injuries such as knees, hands, shoulders, feet and back while training. One might suggest a regimen to increase your physical strength without pain.
I can not overemphasize the tremendous boost one gets in self confidence from adding bulk and muscle to your frame. The first thing we see when we look at another human being is their physicality. We are a shallow species. Some people use weights and others use martial arts training to give them the inner confidence and serenity from having a nice body as the girls phrase it.
Short guys really have an advantage here because they bulk up much faster. Homework guy is very short but powerfully built. He would have done well even without his spumy methods.
That handles the physically insecurities and the girls will swoon. Notice how guys seem to lose their brain when a gorgeous girl shows up? The girls are even more susceptible to muscles.