Saying “I’m not sure” out loud is how people learn your “I’m sure” means something.

Certainty offered constantly turns into noise. If you have an answer for everything, nobody can tell which of your answers are load-bearing, and your confidence stops carrying information. Admitting the edge of what you know does the opposite: it marks the boundary, and everything inside it becomes more credible.

The next time you are asked something you half know, say so plainly and then say what you would need to check. It costs less than you think and buys a great deal. People rely far more readily on someone who has shown they will say when to stop relying.