Markov chains model betting sequences by predicting the probability of transitioning between different states, such as a player's current bankroll or the outcome of a bet. The key principle is that the future state depends only on the current state, not on the previous sequence of events. This allows Markov chains to predict how betting strategies might evolve, focusing on the likelihood of outcomes based on the current situation, such as adjusting stakes after wins or losses, without considering past bets. This mathematical model can help forecast future betting behaviors and outcomes.