The dishwasher will not wash dishes if it had not been set to run.
One might think this is obvious.
I opened the dishwasher this morning to unload it. It had been my habit all week to empty it each morning, so I went to do so without thinking.
It turns out that it was not full last night, so we did not run it.
I wonder how often I react to something with more or different expectations than I ought to have.