Not invented here!
Not invented here (NIH) is the cultural aversion to adopting work that was produced outside one’s own team or organization. The same name is used for the countervailing principle that, when choosing between building something and buying it, we should err on the side of buying.
The instinct is understandable. Engineers are paid to build, and building is often more interesting than integrating. A team that writes its own version of something also gets full control over its behavior, its dependencies, and its roadmap. But the instinct is expensive. Building a component yourself pays not only the initial development cost but also the long-term cost of maintenance, support, and security patching. An external maintainer or vendor would otherwise absorb that work. You also forgo the field testing and edge-case fixes that an established, widely used alternative has already accumulated.
A useful rule is to limit custom development to core domain services, the parts of a system that are unique to your business and provide its competitive advantage. Everything else, from authentication to logging to message queues, is better adopted from a mature library, platform, or service and treated as a commodity. Time spent reinventing a commodity is time not spent on the differentiating parts of the product.
NIH is most often named as an anti-pattern because the rejection of outside work is driven by culture or ego rather than by a genuine technical mismatch. When the decision is made on the merits, because no existing option meets a hard requirement or because owning the component is strategically necessary, the same act of building is sound engineering rather than NIH. The distinguishing question is whether the team is building because it has weighed the alternatives and found them wanting, or because it refuses to trust work it did not produce.
The cultural counterpart to healthy code reuse is a team that can reach for a dependable asset without re-implementing it. Reuse is most productive when that instinct is strong, and least productive when it curdles into refusing good work simply because it came from outside.