Egotistical thinking puts one's own needs above others when, given the circumstances of the situation, they should not do so.
There is, of course, nothing wrong with taking care of yourself. However, when this aforementioned act comes at the expense of delaying or even hindering the helping of others, that is where it becomes a problem, and that problem is at the centre of egotistical thinking - a problem that refuses to be forsaken when the ego dominates the higher self.