When we do not feel we can express as ourselves within our environment, or that we are not acceptable to others, we automatically search for certainty.
If we cannot find certainty on the inside, we find it on the outside, in the form of some balancing force; be it chemicals, a codependent relationship, or whatever distraction(s) we find to calm us enough to cope.
When we go outside, the outside becomes us, just as when we go inside, the inside becomes us (when we are initially searching for certainty).
Until we feel comfortable in both realms, we are imbalanced to one degree or another.
Imbalance is stress, and leads to some form of dis-ease, be it physical or mental.
If people understood this fundamental principle, much heartache, pain, judgement and suffering could be avoided.