I’m fairly certain this question applies to American and Commonwealth armies. Not sure about others.
It is frequently said that a newborn second lieutenant should listen to his sergeant’s advice, and follow it. The 2LT outranks the SGT, but the SGT has far more practical experience.
Are there any circumstances where a 2LT reasonably should overrule his sergeant? If there aren’t, then why doesn’t the rank structure reflect that?
They have different jobs. An officer receives and leads the mission and will bear the responsibility for how it’s performed. A low level officer such as a 2lt usually deals with this on a small scale, such as a single squad. While this puts him close to the NCO’s scope, the NCOs are focused on the inner workings of a squad or platoon. They can give valuable info on individual strengths for specific tasks in the squad and tactical familiarity. A good 2lt will use that and combine it with his higher level approach including logistical concerns ( timing, transport, supplies…), intel about the situation as well as comms with possible other active elements in the area to formulate a strong plan to maximize success chance and minimize risk.
A NCO has completely different training and knowledge from an officer. The whole planning and strategy part, including high level communication and logistics are usually of no immediate concern to an NCO. Still, depending on training and experience, they might have insights on particular fields, and a good officer uses any advantage.