A simpleton is someone who lacks intelligence or good judgment, often making foolish decisions or failing to understand things that others grasp easily. If a character in a story keeps falling for the same trick over and over, never learning from experience, you might call them a simpleton.

This word carries a harsh, insulting edge. Calling someone a simpleton means more than saying they made one mistake: it suggests they lack basic common sense or the ability to think things through. In older books and fairy tales, you'll sometimes encounter simpleton characters who get tricked by clever foxes or fall into obvious traps.

The word feels old-fashioned today. Modern speakers might say someone is gullible (easily fooled), naive (inexperienced and trusting), or foolish (making poor choices), which describe specific problems without the broad insult that simpleton carries. In The Princess Bride, the character Vizzini keeps calling others simpletons while making terrible decisions himself, showing how the word can say more about the person using it than the person being described.

Because simpleton is such a cutting term, it's rarely appropriate in real conversation. Using it to describe an actual person shows meanness rather than honest criticism.