Good and evil.

Selfishness is a concept more often viewed from the "outside." One person lives as it is convenient for them to live (even if this "convenience" is ephemeral). Another person also lives as it is convenient for them, but if the "conveniences" of two people intersect, a conflict arises, and someone must give in. As a rule, the one who gives in is the one who labels the other as selfish; however, in another situation, HE will not give in, and will himself, in turn, become the selfish one in the eyes of the person to whom he did not yield his convenience. Everything is relative... relative to the "victory" or "defeat" of someone's convenience.
If someone takes it upon themselves to care for a critically ill person, they almost certainly consider the patient a "bore," "selfish," "grumpy," etc., internally, simply because they constantly have to "lose" their own convenience for the sake of the critically ill person's. And soon, the person begins to hate this patient with a fierce internal hatred, even though on the outside they may seem like "Mother Teresa."