A lot of apps (old-timey Windows apps, for example) have this philosophy, leading them to reinvent things like crypto and image decoding. Naturally, this leads to tons of bugs, including security bugs.<p>I would revise this to: Don&#x27;t bring in more code than you need. But if the choice is between writing something yourself and using someone else&#x27;s well-tested, heavily-used library, always go for the latter.