Now, every time I fly, I assure a 10 second stop and sanity check, at least once before takeoff - I think I have done everything, but am I sure?
I call this the "idiots check" and do it every now and then during my flying (and in other areas of life, particularly when things get complicated) every now and then.
Basically I'm saying to myself: "I think I am doing something stupid right now. Let's take some time and figure out what."
Usually I'll find nothing wrong, but every now and then I do find something wrong, which I would not have caught otherwise.