i think the distinction exists in most languages - in the case of libraries you are trying to make things easy for callers of your code who's motivations you ca

i think the distinction exists in most languages - in the case of libraries you are trying to make things easy for callers of your code who's motivations you cannot understand; in the case of application code, you probably do have a pretty good idea of how/why people might call it or try to extend/maintain it.