On Who Wants to Be a Millionaire?, a contestant can walk away from or pass on a question if he/she does not know the answer to the question (usually having no lifelines left), to avoid risking losing large sums of money.
When a contestant decides not to gamble on a question, they are presented with the money they have already won and let the next contestant play in the hot seat. Walking away is generally not advised on the first question (as no money has yet been won) or on "free shot" questions because there would not be much point in doing so as the contestant would not lose any money. Although this has not been done, several contestants worldwide have walked away with one or more lifelines still intact - notable examples being Graham Elwell (the first contestant to play the game worldwide, who had his Ask the Audience lifeline still intact), Ben Bartle (who also had his Ask the Audience lifeline still intact), Peter Spyrides (who had his 50:50 lifeline still intact), Danyle Geist (the contestant on Grand Giveaway Week, who had his Phone a Friend lifeline still intact) and Mikhail Boyarsky and Valentin Smirnitsky (who also had their Ask the Audience lifeline still intact).
Walking away is not allowed when a contestant uses the Double Dip lifeline, which requires two final answers and if neither answer is correct or if time runs out on the clock version, the player would leave the game with the last guaranteed prize. Most contestants however strategically use the Double Dip on one of the two "free shot" questions.