Update: My neighbor wandered over while I was framing my pergola and gave me one tip that saved the whole build
I was squaring up the posts for a 12x14 pergola last weekend in my yard in Boise and my string lines were about 3/4 inch off from corner to corner. I kept re-measuring and re-nudging, getting nowhere. My neighbor Ray, who is 71 and has built more decks than I will ever see, walked over and asked if I had checked my diagonals on the holes, not just the posts. I had not, because I assumed the post position was what mattered. He grabbed my tape and ran corner to corner on the footings, found the same 3/4 inch there, and told me to fix it at the source before I poured another bag of concrete. Moved one footing 3/4 inch, reset my strings, and everything lined up in about 10 minutes. If you have a neighbor who has done this a hundred times, what is the one thing they caught that you had already checked twice?