Did you ever watch someone measure a board like five times and still get it wrong? My buddy tried building a shelf last month and kept coming up short because he thought a 2x4 was really 2 inches by 4 inches. He measured the space, bought the wood, and then the boards didn't fit the brackets he got. Turns out the actual size is like 1.5 by 3.5 after they dry and get planed down. He was so mad, he called the store asking if they sold him the wrong stuff. The guy just laughed and said welcome to lumber, man.