You’re in a build headed to the fourth floor. When you reach the second floor, you’ve gone one floor and have two more floors left, so you’re 1/3 of the way. But at the same time, you’re on the 2nd floor and have two more floors to get to the 4th floor, thus you’re halfway there.

This doesn’t work in Europe, because they typically refer to the “first floor” as the ground floor, and the first floor is one story up.

Thanks to Danny Llinas for submitting this.