A pitfall is a hidden danger or unexpected problem that can catch you off guard. The word originally described a trap hunters dug in the ground and covered with branches: an animal walking along would suddenly fall into the pit. Today we use it for any kind of trap or problem that's hard to see coming.

In school, a common pitfall when writing essays is forgetting to proofread: you might think you're finished, but spelling mistakes are waiting to cost you points. In math, a pitfall might be forgetting to check whether your answer makes sense. When learning to ride a bike, a pitfall is looking down at your feet instead of ahead, which can make you wobble and lose balance.

The word suggests something that seems safe until you're already in trouble. When someone warns you about the pitfalls of rushing through your homework, they're telling you about mistakes that people commonly make without realizing it. Being aware of pitfalls helps you avoid them: if you know that a steep hill has loose gravel (a pitfall for cyclists), you can slow down before you reach it.