Gambling is all about random number generation, and provably fair scheme provides guarantees that casino doesn't cheat, but we also know that humans are horrible random number generators - we are very easily predictable.

There are many online demonstrations available, I'll just drop one here: http://www.cs.stir.ac.uk/~kms/schools/rps/index.php
After a small number of games, computer becomes quite good at consistently beating you at the game.

So, theoretically a casino can observe how you place your bets, then predict your next bets and make their own bets (they always go first) accordingly. The flaw here is if this algorithm is implemented too naively, it can be abused by players by making big amounts of predictable low-value bets, and then making a big opposite bet.