<i>Now, some of you may not ever write computer programs, but perhaps you cook. And if you cook, unless you're really great, you probably use recipes. And, if you use recipes, you've probably had the experience of getting a copy of a recipe from a friend who's sharing it. And you've probably also had the experience — unless you're a total neophyte — of changing a recipe. You know, it says certain things, but you don't have to do exactly that. You can leave out some ingredients. Add some mushrooms, 'cause you like mushrooms. Put in less salt because your doctor said you should cut down on salt — whatever. You can even make bigger changes according to your skill. And if you've made changes in a recipe, and you cook it for your friends, and they like it, one of your friends might say, “Hey, could I have the recipe?” And then, what do you do? You could write down your modified version of the recipe and make a copy for your friend. These are the natural things to do with functionally useful recipes of any kind.</i><p><i>Now a recipe is a lot like a computer program. A computer program's a lot like a recipe: a series of steps to be carried out to get some result that you want. So it's just as natural to do those same things with computer programs — hand a copy to your friend. Make changes in it because the job it was written to do isn't exactly what you want. It did a great job for somebody else, but your job is a different job. And after you've changed it, that's likely to be useful for other people. Maybe they have a job to do that's like the job you do. So they ask, “Hey, can I have a copy?” Of course, if you're a nice person, you're going to give a copy. That's the way to be a decent person.</i><p>— Richard Stallman, 2001 (<a href="https://www.gnu.org/philosophy/rms-nyu-2001-transcript.html" rel="nofollow">https://www.gnu.org/philosophy/rms-nyu-2001-transcript.html</a>)