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

NEVER believe for a minute that anyone else in the military will watch/monitor your career as closely as you do yourself. NEVER assume someone will automatically promote you or enter your name for any program, school, or advancement opportunity. NEVER throw away ANY military paperwork. Many were the times during my 30 year military career that I had an order or piece of paperwork that DA or my unit had supposedly 'lost.' I simply kept a file drawer with plain manila folders marked by year and tossed a copy of anything into them. So - one folder for each year takes up very little space - or if you're a computer nut - scan them and keep those scans on more than one back up drive or thumb drive. This was some of the best advice I ever received as a young enlisted soldier, then Warrant Officer, and finally walked out the back door as an O6 Colonel. I found an award I had never received, corrected retirement points and dates, successfully challenged incorrect verbiage on more than one efficiency report, and was ALWAYS up on promotion times, requirements and submission items. Having all my admin ducks in order got me promoted at first look and I had my name first on the list for any required class or school. Simple advice, simple process, simple program for success in one's military career.

When I was a PFC, maybe a SPC I can't remember exactly, I was tasked with a detail for a change of command that took place at III Corps. I was an usher; basically, I took the place of a cone marking the way to the reception. I was just supposed to stand at parade rest and whenever someone passed me I would come to attention and render a greeting. Eventually, a CSM and a BG came walking up to me. I went from parade rest to attention and rendered a greeting. They BG raised his hand above his head for a high five. I stood motionless at attention for about fifteen seconds before the CSM leaned in and said, "unless you want to do some push-ups, you better give that general his damn high five, private." Well, there was no arguing with that. I reluctantly gave a pitiful high five to the BG and quickly snapped back to attention. They both smiled and as they began to walk past me the BG chuckled out, "Don't take life too seriously, kid."
Words that I have lived by ever since! lol

I was deployed to Iraq and I'd just pinned E-5. I was tasked with driving the task force CSM to the flight line at BIAP. After several minutes of awkward, silent driving I worked up the courage to ask him if he had any advice for a new NCO. He simply said to leave every assignment a little better than when you arrived. Even if it's a small improvement eventually it all adds up to something much bigger.