My friend, I find that the gullible are those who close their minds to new ideas. They only want to hear things that conform to what they already want to believe.

But those who are open to new ideas are less gullible. They are more used to evaluating new ideas, testing them, finding out what is true, comparing claims to see where the truth lies.

In my experience, no one is more gullible than someone who thinks they have a lock on the truth, and assumes that everyone who disagrees with them can only ever be wrong.