Verifying code and reading it aren't the same thing. And yes, most developers don't verify their code as carefully as they should. But also, there are blind spots to verifying your own code because brains take shortcuts. At the same time, there are difficulties verifying other people's code because of different shortcuts brains take.
There was a simple function in java standard library which was wrong for years because of this phenomenon.
what? so people just write code and never read it back?