Best hobby advice you've received.

[FrankWakefield]

When you're the winning high bidder at an auction, you can be certain that you were paying more than every other person interested in the item.

Acquire two of everything, then you'll have one to trade.

Know what you're buying, know the cards; do not trust the grading companies.

Collect the cards, not the slabs.

When buying 1952 Topps as a kid, I'd have made more money if I'd thrown the cards away and safely kept the wrappers and sold those now, rather than have kept the cards and discarded the wrappers. (I paraphrase what and older collector told me about buying 52 Topps, wasn't around then.)

When working on a set, if you buy a filler card that you're not happy with, you'll end up buying that card twice. (I can remember this, but I've disregarded it a few times, so that I experienced negative reinforcement when I ended up buying a better version of the card.)

It's a hobby, it's just cardboard; it's not an investment.