Rejection sucks, and the damage it can do can be catastrophic. This rejection loop is often played out when Military members try to transition to civilian life, but that's not the only place where we see it. 

Anyone who is a little socially awkward can experience rejection, which puts them in isolation, which makes them more awkward, which causes more rejection. 

Rejection-Isolation-repeat until someone becomes either a total recluse, or unable to function in any social setting. 

When this happens, people will either become wall-flowers, or they will lash out / act out.  Often, they simply isolate, and avoid people at all costs.