A behavior that parents find disheartening is their teenager's tendency to form rapid judgments about friends. Quickly deciding if a friend is "good" or "bad" and, if the latter, instantly removing them from their phone and online "friend" status.
Yet this behavior is analogous to that of infants who relate to their mother in black/white terms, whether or not she satisfies their momentary need. Only after maturing can a child relate to others in terms of shades of gray, understanding that one can possess both good and bad characteristics.
Similarly, the teenager whose personality is slowly developing into their fixed adult structure, requires maturing to accomplish this anew, and some with emotional difficulties never do.