These are far from the only possible pairings, however, as virtually any story with multiple characters can contrast the characters to show greater depths to them, regardless of what side they are on in the good versus evil equation.Good versus evil doesn't have to come into the picture at all.
More often, though, the foil is a recurring character that has a personality, or an opinion of things, that is different from another recurring character.
It is inevitable, the feeling of hopelessness, sorrow, or being alone.
These are all common emotions associated with depression.
Yet the question remains, why did these people become depressed? One of the answers that lead to the cause of depression would be a person's interpersonal relationship with their surroundings and the people around them.
There are many interpersonal instances that can have the ability to lead to the onset of depression, such as the family environment, the socialization setting, and the discrimination against gender in certain cultures and instances.