You are in a spaceship. There are two identical red buttons. One will land the ship safely, and the other will cause a catastrophic error which will cause the ship to self-destruct. You must choose which to push.
With you on the spaceship are two friends—both are experienced space travelers—and both know which button to push. Unfortunately, one always lies, and the other always tells the truth. You don't know which is which.
You have to press a button in 10 seconds, or you will go hurdling into the surface of the red planet.
What question do you ask to help you press the correct button?