You have to take one each of two types of pill every day. If you fail to take one of them, or take more than one, you will die!
Unfortunately the two types of pill look identical. You have two days' worth of the pills (that is four tablets) and you drop them on the floor. You have no way of knowing which of the pills is which type.
How do you survive until the next delivery of pills?
Cut all four pills in half, putting the two halves of each pill in separate piles. Then consume one pile of four halves today, and the other pile tomorrow.