The expression, "Somebody has to be the adult," has gained wide usage and for good reason. In too many situations, individuals who have embraced the idea that feelings should trump logic, wisdom, and experience choose to act like children.
They throw fits, bully, and call names. They hold absurd grudges and disrupt serious deliberations. They are more interested in venting their emotions than in attaining any semblance of effectiveness. They fail to realize that "Be yourself" is not always sound advice. Often, the wiser course is "Be better than yourself."
I've seen people who want to fashion current policy in reaction to a dispute that took place 20 years ago and which no longer has any substantive relevance. They aren't like the general who wants to fight the last war; they are like one who wants to fight the war before the last war.
These are not people of little talent. In some realms, they are very competent and insightful. They do, however, lack the sound judgment that is needed to lead. They don't know how to act like an adult.