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

GREAT question!

If you get visibly angry and full of rage in peace, you just sent a message you don't want to send about how you will be in combat. I never allowed myself to be angry with a Marine again.

You need to make sure that your family comes first in all your decisions because if no matter if you do 4 years and get our or do 20+ and retire your time in the military will eventually come to an end and your family will be all you have left when your military career eventually ends.

At my first duty station, during my very first debrief my SNCO gave me advice that I followed throughout my career. He stated, "You can't be a good leader if you're not a good follower" that click with me instantly because it made sense to me. I was lucky in my career because I had good NCO's & Officer's I respected, here is one more example that was profound to me once I became an aircrewman, my Commanding Officer told me "Whatever you do when people are around doesn't matter as much as to what you do when people are not around." While I have many other's these two were the ones that shaped who I was while I was servicing our great country.

That's simple....lead by example!

A Captain I served under was instructing a newly arrived Ensign to earn the respect of those who serve below deck. The Ensign looked perplexed and ask, "Why is that?" The Captain, amazed at his arrogance, sternly replied, "Because they're the ones who know the ship is sinking first!"

Th best lesson I learned was early in Beast Barracks. We were in the middle of a uniform formation drill. There was no winning only persevering. The fact the entire process was not win able wasn't the point. The point that I took away was we were going to keep going regardless of the outcome and we were going to do it together. Keeping one's cool under pressure served me in good stead flying fighters and in the courtroom once I quit flying.

An organization does those things well that the boss checks. So as a boss, you need to check everything. If not the boss, you need to check everything that the boss doesn't.

That the work will always be there tomorrow no matter how late you stay that evening. I was always staying late trying to either get ahead or complete another task. It will eventually catch up with you...maybe not tomorrow, or next month, or next year, but somewhere along the line you will hit the wall.

I was at PLDC in Bad Toelz and the Commandant of the NCO Academy popped into our class one day for a chinwag - Q&A session. Some bright spark in the class asked him "If you could go back in time and give yourself one piece of advice on the day you made sergeant, what would it be?"
The Sergeant Major -- for the life of me, I cannot remember his name but he was a CMH recipient - said this: "Never give an order you don't expect to be obeyed."
It took a few years and a lot of frustration for me to really understand the sheer depth and wisdom of that advice. Once I did, his words changed not only my style of leadership but life as well.