A gamble feature lets you stake a win you have just landed on a simple guess, typically red or black on a card for double or nothing, or suit for four times. Guess right and the win grows; guess wrong and it is gone.
It is optional and usually offered only after a base-game win. Where the guess is a true double-or-nothing at even odds, the gamble does not change your expected return. What they do change is the spread: taking the gamble turns many small wins into fewer larger ones or nothing, which raises volatility.
No guessing pattern helps, because each guess is decided by the RNG. Not every version of a game includes the gamble feature, so check the paytable. Fruit machines had a similar step, often a hi-lo gamble. See our gamble feature page.