When someone presents you with a question you should know the answer to, our reaction is to respond whether or not we really know. It’s hard to say “I’m not sure,” as it inherently comes with the feeling of being in the dark. But if the fact is you are unsure, admit it.
Quickly spewing an answer you think is correct can be dangerous, and if you’re ultimately wrong will color you untrustworthy. If you’re not 100% sure, find out before giving an answer. A delayed yet accurate answer is far better than a hasty mistake.