What are the lessons people most often learn too late in life?

Save every penny you can for later in life when you'll need it most.

When you hand your beer to a bystander & tell them to hold my beer & watch this your beer is always empty when you return from doing your trick.

I would say anything relating to debt and trying to stay out of it. 

If you borrow from someone at least borrow into equity is my advice - although I'm certainly no Wall Street maverick. 

I base this answer on being again, in debt, having been played by creditors who know people spend emotionally and who know that emotional spenders DO have a conscience. 

That life is a terminal condition.

Stop being so stubborn

Time is precious, don't waste it