You decide that, in order to save a bit of money, you're going to set your printer to always print in black & white (in other words, grayscale). So the next time you print a document in Microsoft Word, you go to File>Print..., and check the "Print in Grayscale" box.
And then the next time you print, it prints in color. Why?
Because you changed the feature while you were printing a specific job. The way your printer driver is programmed -- the way all printer drivers are programmed -- any changes made while you're in an application -- Microsoft Word, say, or Excel, or any software at all -- that change will only apply to that one specific time. The next time you print, all the features will be back the way they were.
The way to make a permanent change (or, at least, a change that will last until you yourself change it back) is to access the printer driver through Control Panel. (For information on how to do that, see Step-By-Step: Find Your Printer Driver.) Any changes you make in your driver at that point will apply to all the printing or scanning jobs you do from then on.
