A pattern I’ve noticed in every smart person I know:

They’re devastatingly confident on the things they actually know.
But the second the topic moves outside their expertise, they go quiet and start asking questions.
They're curious, want to learn, and accept being challenged with new information.
The dumbest (pseudo-smart) people do the reverse - they think they're an expert on everything. To me that’s the biggest red flag there is.
Accepting when you don't know something isn't a weakness, it's a sign of intelligence.