Kelly Can't Fail

I was like "oooh fun a card game" then was like "oh shit I'm too dumb for this math"

You aren't dumb. You just don't have enough exposure to the prerequisites.

It could also be both: though it's not necessarily that they are "dumb", but that the language of mathematics is something they can't get their head around, even if they can understand the concepts when described in spoken language.

Eg. it's probably pretty easy to convince them that with 15 cards in a deck, out of which 5 are red and 10 are black, chances are bigger (and in particular 10/15 or ~67%) that they'll pull out a black card, and that you should bet more on this happening. If you happen to miss, you should only bet even more on black since the chances grow further — to be able to maintain this strategy, you only need to never bet too much so you have enough "funds" to bet all the way through (eg. in the worst case where the least likely thing happens: in my example, that would be 5 red cards coming up first).

Putting all this reasoning into formulae is what math is, and I do believe some struggle with abstracting these more than others (which is why the divide does exist and why many people believe those good at math are "smart", which is very much not so — seen plenty of "stupid" mathematicians, even professors). Does not make them "dumb", but might make them "modern math dumb". A signal that someone can be good at math today is that they are unfazed with more-than-3-dimensional spaces (you need to stop tying things to physical world).