I was REMINDED that most of my mistakes happen at the end of day, especially when I'm in the mindset of " I'll just get this much more done today, so I'll be ahead tomorrow."
On this project I was cutting window stools. I used test pieces to figure the offset of the casing, the wing of the stool beyond the casing and then added that x2 to my window width measurement. Cut one, did the returns, and happy with the way it looked and fit, measured the other windows and started my cut list as I went. Problem was that I put the width and a +, but forgot to add the trim x2 before I cut . . . . Even though I kept looking at my cut list for each length before sawing . . . . . This, of course, was at the end of the day. Why the "+" sign didn't jump out at me I do not know, but doubt it is because my ADD suddenly went away . . . .