You aren't stupid for a mistake such as this.
There should be room for workers to make so-called
honest mistakes. In businesses that expend people
as often as you imply here, the product of said
businesses tend to suffer as well. There are some
ways to manage workers that are better than others.
Also, what kind of an environment would that be
(the one that puts so much emphasis on accuracy)?
People have this idea that you have to do things
you don't want to do: "that's just reality." And,
unfortunately many people fall for this capitalist,
individualist dellusion.