We all make mistakes. Well, I don't, but everyone else does (ironic smile here). You would think that after all the years that humans have been making things out of wood, by now we would have figured out all of the ways to screw up. That there would be a "knowledge base" of all the possible errors that we could refer to and by doing so, avoid having to reinvent the wheel. But not so. It seems that mistakes are like chess the possibilities are endless. We are constantly finding new ways to generate scrap.
And it's not just the undiscovered mistakes that get us. Some mistakes seem to have a way of repeating themselves over and over. OK, I should restate that. We have a tendency to make the same mistakes over and over. They don't "make themselves," as much as we might want to think they do.
One of my favorite mistakes is to pull my tape the wrong way so that the numbers are upside down and then read the sixes as nines and vice versa. If I'm lucky, this results in a piece that is 3 inches too long which at least still yields a useable piece even though it requires re-cutting. But more often than not, the error goes the other way and my piece is 3 too short.
Another very popular error results from the common practice of "burning an inch" when using a tape. Then you forget to add the inch back and bingo another piece of scrap hits the floor (or the wall). Or how about building an entire set of cabinet drawers but forgetting to deduct an inch from the width to accommodate side-mounted glides?
Then there is marking a piece and cutting on the wrong side of the line. This results in a piece that is too short by only the width of the kerf. Most of us only do this when we have no more wood left.
When I used to build houses, there was always a "transition period" when we went from framing to finish work. The first few days of woodwork always had "moons" because we had not yet cleared our minds of the need to really bash the nails to "set" them. Then, when we went back to framing, we would spend the first couple of days carefully tapping the nails in.
And then there is something that is more of an axiom than a mistake the first piece you cut will always be wrong. For me this axiom goes a bit further in that the last piece will also always be wrong. Don't ask me why. That's just the way it is. While I have never been able to escape this, I have learned to always have just one more piece available...