In my work as an addiction counsellor, I often encounter issues of shame behind substance abuse. The influence of shame on self-destructive habits looks something like this:
A person grew up with a belief that he is unworthy, damaged or a bad person. He struggles with the pain and fear generated by this underlying belief and attempts to invalidate the belief through his actions and behaviours. At the same time, because he has not reconciled his fear of this belief, he tends to perpetuate acts that substantiate the belief.