Also, beer example was just meant to highlight that friend we all have who practices "selective accounting" with our informal running tab. If I had any suspicion that $3 is make or break to someone I would gladly pay them what's owed and forget about the beer. Beer (and all vices really) have their own set of norms.
So I worked at a factory and he was a notary or some such function connected with real estate, working from home. One day I was running late for work, which was maybe fifteen minutes away by bicycle, and asked if he didn't mind giving me a lift. About halfway there he mentioned casually, "Oh, just so you know, I'll be billing you at my normal rate ($60/hr) for this ride." Thanks for the trouble, just pull over and I'll walk, buddy.
People may or may not have sane ideas about friendship and money.
"I can't, I'm busy right now."
That's what people say when someone asks them to do something they don't want to, or where the cost outweighs the benefit.
If someone grabs a tab and sends me a Venmo bill, I'll happily send them their money. I would have rather grabbed the tab the next time. I won't be doing both.
(And vis a versa - If I say "I've got the tab" and the person sent me money, I'd be much less likely to invite them out in the future. I'd rather they just invited me out and grabbed a round.)
It took me a long time to learn that when your friend's dad tells you 'Please just call me John', continuing to address him as 'Mr. Smith' is less polite, not more. Same thing with money.