A math professor wrote a book on how to beat the casino at blackjack.

The key difference from roulette:

In roulette, each spin is independent.
In blackjack, cards are dealt from the deck and do not go back in. The deck "remembers".

If many small cards (2-6) have already come out, then there are more big cards (10, J, Q, K, A) left in the deck.

Big cards are good for the player because they increase the chance of hitting 21 and the chance that the dealer busts.