Shortcuts don't always work when laying out miters
"Since almost anyone can cut a square miter, the question at once arises, in view of this statement, why is it he cannot cut a raking miter, or pinnacle miter, or any other equally hard form? The answer is, because he does not understand how he cuts a square miter. He may perform the operation just as he has seen someone else do it, or as laid down in some book or paper. He may produce results entirely satisfactory from a mechanical standpoint, but after all is finished he is not intelligent as to what he has done, he does not comprehend the why and the wherefore of the steps taken."
- From The Metal Worker Pattern Book by A.O. Kittredge, 1881.