To assume means to accept something as true without proof or verification. When you assume your friend is angry because they're quiet, you're deciding that's the reason without actually asking them. Maybe they're just tired or thinking about something else.

Assumptions can lead us astray. If you assume a test will be easy and don't study, you might be unpleasantly surprised. If a teacher assumes you didn't try hard on an assignment when you actually spent hours on it, that assumption feels unfair because it's wrong.

The word can also mean to take on a responsibility or role. When someone assumes leadership of a group project, they're stepping into that position. When a vice president assumes the office of president, they're taking on those duties.

Instead of assuming you know what someone meant or how something works, you can ask questions and gather facts. Scientists design experiments specifically to test their assumptions rather than just accepting them. The phrase “don't assume” reminds people to check the facts rather than jumping to conclusions based on incomplete information.