Probably also learned tolerance. I have a German friend come over once and in Germany they basically drink the same coffee (we call it black water here) as you guys in the states. You know, those normal huge 200ml jugs.
So one day I meet him at a cafe (around 6mp) and we chat awhile and drank coffee. He never had drunk an espresso before (imagine that lol) and he liked it so much he drank two.
I told him he probably should only have one as he wasn't used to it.
He said it wasn't a problem because he drank tons of coffee back home.
I told him Well, pressing boiling water at 4 bars through 5gr of pure coffee into a 10ml cup has a little more than an entire pot of coffee but he just smiled and ignored me.
The next day I met him at lunch and I notice black rings around his eyes lol. He didn't sleep all night walking in circles in his room.
Me, on the other hand, can drink a expresso right before going to bed and it doesn't affect me at all... But I'm doing this for 24 years so I guess there is tolerance.
Some of my friends don't drink coffee after 4pm.
Regards
Tony
Sent from my keyboard through my phone or something like that.