My old supervisor in Galveston bet me $50 I'd never pass my ADCI surface-supplied eval on the first try
He told me to slow my descent on the helmet check because I was rushing the equalize and blowing my ears out on the way down. I did pass first try, took his $50, and then had to buy the crew lunch with it anyway.
What's the one piece of dive advice you got that actually held up under pressure?
Watched a buddy learn the hard way on a rig job down in Fourchon. He kept his mask too loose thinking he could clear it faster and took a nasty face full of water at 60 feet. The tender told him to tighten the straps and stop being lazy about the seal check before every splash. He still does it to this day, every single dive, no shortcuts.