“Never underestimate your listener's intelligence, or overestimate you listener's information.”
“Never underestimate your power to change yourself; never overestimate your power to change others.”
“A friend should always underestimate your virtues and an enemy overestimate your faults”
“It is as much of a mistake to underestimate yourself as to overestimate yourself.”
“Most people overestimate others' talents and underestimate their own.”
“There was a survey done a few years ago that affected me greatly. it was discovered that intelligent people either estimate their intelligence accurately or slightly underestimate themselves, but stupid people overestimate their intelligence and by huge margins. (And these were things like straight up math tests, not controversial IQ tests.)”