I had a buddy who was a blackjack dealer. He explained it to newb players like this: "dude, you can do that, but if you had an 18" dick, would you cut it in half?"
Now, knowing /badwomensanatomy, that's passe', but it stuck with a younger me.
So it's kinda like "quit while you're still ahead" type of deal? I don't think any type of gambling parabolas can be good advice considering, well, the nature of gambling.
No, it's not something that is meant to be broader advice or a metaphor for something else, it's literally advice for playing blackjack. What they're saying is that it isn't actually a good idea to split on an 18 when playing.
Split is a move in blackjack. It's not just hit and stay.
You turn your 9-9 into two separate hands starting with 9s. The most likely card in blackjack is a ten cuz of all the face cards, so the idea is you get 19s instead of 18s
However according to blackjack cheat sheets you should not do this if the dealer is showing 7 10 or A.