The view of Maimonides is that hitting the rock was not in itself the sin, but the fact that Moses lost his temper. Leaders should keep their cool.
Personally I learnt this lesson from a community leader whom I knew as an even-tempered chairman who could not be ruffled despite any provocation. There was one occasion when he did lose his temper with a certain board member and I asked him how he could have let this happen. His reply? “You’re right – I never lose my temper… except on purpose!”
Leaders face agreement or disagreement with the same equanimity. When Moses erupted and called the people rebels (another view says, “fools”) he deserved punishment.
Another rabbinic view is that in hitting the rock, Moses deviated from the Divine instructions. God told him to do one thing, to speak to the rock, and Moses did another: he hit the rock.
A leader remains constant and consistent. He does not waver in the wind. If God, the Leader of Leaders, gives him his briefing, a leader follows and keeps to the brief.