system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly is "counting cards"?

Ben Affleck was busted doing this in a casino in Vegas. What is it exactly? And is there any way for casinos to guarantee that no one does this?
gpt
Start at zero.

When you see a 10 card (10-K) subtract 1 from the count.

When you see a 2-5 add 1 to the count.

When the count hits something good like maybe 12 or 15 raise your bet to the max.

That is the short answer.

The reason being is 10 cards are when you want the deck to be full of and not a bunch of 2s 3s 4s and 5s (they help the dealer not bust out).

/shrug

The other answers go into much more detail but this is the simple version.

Enjoy.