Exactly this. A dev comes all bright-eyed and bushy-tailed and says we can save a week on the project if we use this open source library instead of writing it o

Exactly this. A dev comes all bright-eyed and bushy-tailed and says we can save a week on the project if we use this open source library instead of writing it ourselves. But he or she doesn't see that they are committing the organisation for the lifetime of the project for someone to keep on top of patches, resolve any breaking API changes, even fully maintain it if the original developer loses interest - or ditching it and writing our own anyway. There is a lot of great open source around, but it is by no means "free" when you look at the big picture. This is one of the key differences that marks a senior from a junior engineer. You can see the junior's eyes glaze over when you try to explain it and you know they'll be back next week begging to use something else they read about on Twitter or HN...