I find the most common "stupid" mistake I make in writing can be titled the I Knew What I Meant mistake. For example, my alpha reader will say, "What's your detective talking about? He's referring to his notes, but notes from where? From whom?" I say, "From the people at the fireworks, of course." And he says, "Well, maybe you know that, but you've got to tell your reader that." And my mind says to me, "Duh!" because he is absolutely right and I have made that stupid mistake again.
I use "stupid" mistake to distinguish this type of error from my other "careless" mistakes, "inaccurate" mistakes, and "bad writing habits" mistakes. To name only a few of my mistakes.
The big lesson in this post is that a person should always, always have readers. Bless them!