I was talking about both. Sometimes even in a problem space time constraints demand that you utilize something off the shelf (whether you use part of it or build on top of a custom version of it).
Tools aside, I think everyone who has 10+ years can think of a time they had a prototype go well in a new problem space only to realize during the real implementation that there were still multiple unknown unknowns.
Tools aside, I think everyone who has 10+ years can think of a time they had a prototype go well in a new problem space only to realize during the real implementation that there were still multiple unknown unknowns.