What’s Up with That: Why It’s So Hard to Catch Your Own Typos

"what we see on the screen is competing with the version that exists in our heads."

Greg: "Bill, I know there is a bug in this code block, the output is transposed. I've been staring at it for an hour and I can't see it."

(8 second pause)

Bill (pointing at the screen): "You left out the second '+' in your incrementer."

Greg: (dumbfounded silence)