The human mind is amazingly resilient, helping humans deal and cope with practically all sorts of things, from the mundane concerns of everyday life to events that bring significant stress.
There are times, however, when an experience is simply too severe to process, and the mind is unable to cope with it. This is when post-traumatic stress disorder (PTSD) sets in, and it is a serious disorder that requires quite a bit of therapy to deal with it.
If not addressed promptly or properly, people tend to find other ways to deal with the condition, such as substance abuse. This is why many are afflicted with PTSD and addiction at the same time.