Hazard for the unwary

PITFALL

A hidden drop that might catch you off guard if you’re not watching your step.

"Hazard for the unwary" hints at something dangerous that catches people off guard, which directly describes a pitfall—a hidden or unexpected trap. The word itself breaks down neatly: a pit is a hole in the ground, and fall is what happens if you don’t spot it in time. It’s also a common metaphor for mistakes or problems that aren’t obvious at first glance, making the clue work on both literal and figurative levels.