If I had to pick one thing as the "lesson i have learned that has had the most far-reaching benefit in my adult life", it would be this: that my own time, effort, comfort, energy level, and physical ability/pain levels are a resource that I must account for in my calculations of utility/benefit, and that it is eminently logical
to trade other resources (money, most specifically, but other things of value as well) to safeguard/benefit those things.
This goes all the way back to the days when I first moved out into my own apartment and "doing laundry" was either a) spending all day in the dank and miserable (and creeeeeepy) apartment complex laundry room with 2 washer/dryers that only took (a lot of) quarters and had no change machine, b) hauling everything to the laundromat and spending all day babysitting the laundry, or c) hauling everything to the laundromat, dropping it there, and paying $.85/lb for them to wash, dry, and fold it, then coming back a few days later and picking up a sack of clean clothes. (I chose C. A lot.) Today, that equation is made manifest in things like paying the fees to sit in the airport lounge whenever I have a layover of more than an hour or so (peace and quiet, better snacks, power strips, fewer screaming children, etc) and decisions like "if it's going to take more than X amount of time to fix the thing, get rid of it and get a new one".
Sarah often says that the lesson that time has value is one of the things she's learned from me that she finds most valuable. A while back, I found a calculator
that tries to put a dollar value on your time. It's a really interesting exercise, for all that it doesn't map onto my life exactly. (I value my free time a lot more than my current hourly wage, but that's partially because it's really freaking hard
to calculate my current hourly wage.)