Where the answer is not just the right answer, but the wrong answer that's also right.
Take one ball out, and look at its color: Red, Blue, or Green.
Now, you have two balls left, but which two?
Take a chance, try to guess!Maybe you should've taken the other one, the one that's not the one you took.
Now, you're back to 3 balls, and you don't know which one is the correct one.
Solve it again!