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.
— Richard Stallman