Depending on what kind of software we are talking about, all kinds of things might change. Hardware and software environments evolve, legal requirements change, it really is an endless list of things that you can not control. Could you have written an image editor 30 years ago that would be usable today when you had less RAM than the size of an images coming from a digital cameras today and in an image format invented years later? Could you have written a text editor useful today before Unicode was invented? Could you have written a tax software that anticipated all relevant taxation changes 20 years into the future? Could you handle touch inputs well before smartphones were widely used and deal with the differences between desktop and mobile in general? Keep up with the changes to HTTP, HTML, CSS and JavaScript without updating your browser?