The intelligent person assumes that everyone knows pretty much what s/he does. They don’t underestimate people, they don’t think they are brighter, they don’t think they are the font of all wisdom.
Simply put, the person with a Ph. D in anthropology is not dead certain of anything, as new findings can alter a long held belief.
The person who just entered college and is taking Anthropology 101 is sure s/he knows everything and is dead on certain of whatever was read in that text.
The ‘give away’ of stupid people is the way they pontificate as if they know. This is because they are ignorant of how much they don’t know.
Once you realise that you know little you are not as confident as the fool who is stepping off the cliff.