Imagine you are in a big, mysterious room with two doors. Behind one door, there's something very scary, and behind the other door, there's something nice and safe. You really want to choose the safe door, right?

Now, in front of each door, there are two guards. One guard always tells the truth, and the other guard always tells lies. But there's a problem: you don't know which guard is which, and you also don't know which door is safe.

So, you need to be really clever and ask just one question to make sure you pick the right door. Here's the question you can ask: "If I were to ask the other guard which door leads to safety, what would he say?"

Now, think about it this way: If you ask the truth-telling guard, he will tell you what the lying guard would say. And if you ask the lying guard, he will also tell you what the truth-telling guard would say, but because he always lies, he will say the opposite.

So, no matter which guard you ask, their answers will be the same! If they both think the other guard would say the scary door, they will both point you to the scary door. If they both think the other guard would say the safe door, they will both point you to the safe door.

This way, you can be sure that whatever door they point to, you should choose the opposite one. So, if they both point to one door, you should go through the other door, and you'll be safe!

You did it! You asked a smart question and figured out which door to choose to stay safe. Great job!