You are hanging a shelf in your daughter’s room. There are holes on the back side of the shelf that mount on screws in the wall. You carefully measure the distance between the center of each hole. You recheck your measurements a second and third time, just to make sure. You mark the spots on the wall where holes need to be drilled with your trusty level and ruler. You drill the holes in the wall and insert the mounting screws. You pick up the shelf and mount it on the screws – only you can’t because the screws don’t match the holes. You survey your surroundings to see which object in the room would be best for practicing a ritual killing on your wall. Seeing that driving a screwdriver through the wall will not improve the situation, your mind downshifts into damage control. You decide that you could drill more holes a safe distance from the old holes, and still cover up the old holes with the shelf. Having tried and erred, you decide to try something else. It turns out that something else works.
There is no feeling in the world like turning a ten minute project into a one hour project.