Because they like to lie to themselves cause their brain is tiny. Majority of them would tell you how they found themselves in those words but it's the opposite.
And yeah, these girls mostly do it cause they're pretentious and want to seem smart and wise, above all infront of themselves.
With boys it's mostly not that they're any smarter, but that they just don't care about pretending to be smart. You'll find a lot more fake gangster badass attitudes with them though.
