Egoism is more of an "external" concept. One person lives in a way that is convenient for them (even if this "convenience" is fleeting). Another person lives in a way that is convenient for them, but if the "conveniences" of two people overlap, a conflict arises, and someone must give way. So, the one who yields usually judges the other as an egoist, but in a different situation, THEY will not yield and will, in turn, become an egoist in the eyes of the one to whom they did not yield their convenience. Everything is relative... relative to the "victory" or "defeat" of someone's convenience.
If someone takes on the care of a seriously ill person, they almost certainly consider the patient to be a "bore," an "egoist," "grumpy," etc., simply because they constantly have to "lose" in their own convenience for the sake of the seriously ill person's convenience. And soon, the person begins to hate this patient with intense hatred inside, although outwardly they may seem like "Mother Teresa."

