You're in a room, with nothing in it except two robots. One robot always tells the truth, the other always lies. You don't know which is which.

There are two doors leading out of the room. One leads to certain death, the other leads to freedom. You don't know which is which.
You can ask either robot a question which will help you get out of the room. What is that question.
(Remember, you don't know which robot is which!)

You ask either of the robots "What would the other robot say if I asked it which is the door to freedom?"

If you as it this question, you will get the same answer from either robot. This is because the truth robot would want to tell you the truth, but because the other robot lies, it would have to lie too.
If you asked the liar robot this question, he knows that the other robot would tell the truth but he would lie.
So if you asked either robot that question, they would both point to the door to certain death.