What is the best lesson an NCO/Officer has ever taught you?

As a young Airman in a Radio Maintenance shop, my Shop Chief taught me the most efficient way to troubleshoot. He called it "Half Split". Using a block diagram of the system, we started in the middle to see if there was a signal. If not, we did the same from there to the end of the circuit, or vice versa if there was a signal. Only when we localized the issue to a block (module) did we open the pertinent schematic. From there we executed the same process. Very fast, and very efficient. To this day, I still use this technique, and I also teach junior level techs and engineers to use it.

Not the most important career-wise, but as far as leading Soldiers, here is the most important advice I received.. Basically I was a newly promoted CBRN SGT in an Infantry Pathfinder Company just being reactivated that only had about 10 Soldiers total, so at the moment of this lesson, the NCO support channel was 1SG -> Me -> junior enlisted, and I was expected to act like an 11B SGT. I was in charge of getting the 5 junior enlisted ready for step off for an early morning ruck march, and long story short, they didn't have proper gear (about -10 degrees in fort drum). So while the Soldiers were sent back into the Company to get their gear, I got a personal ass chewing from the 1SG, that included these 2 gems that I will probably always remember.. "Your Soldiers either want to BE you, or they're laughing AT you. There is no in between." and "It's call 'Pre-Combat Checks and Pre-Combat Inspections', not 'Pre-Combat Surveys.' SEE and TOUCH the equipment, don't ASK if they have the equipment." When it comes to leading Soldiers, those 2 quotes have served me better than probably anything else I've ever been told.