When most people invent something they do so in hopes of making money. But what happens if you invent something that is totally for selfish reasons. -And why not. If you come up with a great idea on how to keep ice off your windows and love it, why not use it. No, you do not have to try and market it, but why not invent it and perfect it for your own use. Just because you have a new idea for something does not mean you end up having to try and manufacture them full scale to sell. There may be nothing wrong at all with using your own invention for yourself.