This isn’t so much “lessons learned” but more so, handy quotes and expressions that are relevant to the hobby (and maybe life), and cut right to the core.
Let’s share 'em here. Hopefully this thread won’t be entirely “SMPratte-isms”, but there is of course the original:
“Older. Rarer. Minter. Better.”
From this month’s MMR.
“Do you have to pay taxes on the trading cards you sell? Man, that’s tough. Since I have to say yes or no, I’m gonna say no.”
“Energyyyy…….ENERGYYYYYYY……”
??? 
“It’s about what you do with what you have, not how much you have”.
From “what is a serious collector”.
Today’s price is tomorrow’s discount." - Alpha Investments.
“Hang that up on the wall next to your Spice Girls poster”
You mean gleaned, not gleamed
Overheard someone singing Pats(deep pocketmonster) “should I open it” song, it was some other type of tcg pack but they kept walking out of earshot and line of sight so I’ll never know the end results 
Wheres the cheaper option?