Most cognitive biases have a psychology lab origin story. This one comes from engineering management.

In 1982, Ralph Katz and Thomas Allen at MIT’s Sloan School studied 50 R&D project groups inside a large lab. They were looking at how team tenure affected performance. What they found was a curve. Groups got better for about a year and a half, held steady for a while, and then started sliding. By the five-year mark, performance had dropped noticeably.

The reason wasn’t burnout or boredom. It was communication. The longer a group stayed together, the less its members talked to people outside the group, including the outside sources they most needed to hear from. Katz and Allen described the pattern as a stable team coming to believe it held a monopoly on knowledge in its field, and rejecting outside ideas as a result. They called it the Not Invented Here syndrome, borrowing a phrase engineers had already been using as an insult for years.

That’s the founding study. Since then, the research has mostly lived in innovation and knowledge management journals rather than psychology.

The most useful modern framing comes from David Antons and Frank Piller at RWTH Aachen University. In 2015, they argued that Not Invented Here isn’t really a behavior. It’s an attitude, a standing negative feeling toward knowledge that gets labeled “external.” And “external” turns out to be flexible. Knowledge can feel foreign because it came from a different discipline, a different department, or a different location. Any of those boundaries can trigger the reaction.

That’s the part worth sitting with. The bias isn’t about ideas being bad. It’s about ideas being theirs.

Why does the brain do this? A few overlapping reasons, and I’ll flag that this next bit is synthesis rather than a single study.

First, ownership feels like competence. If our team built the thing, we understand it, we can defend it, and we get credit for it. An outside solution offers none of that, even when it works better.

Second, evaluating outside work is expensive. Learning someone else’s approach means admitting you don’t already know it, and building your own means starting from what you do know. The second path feels faster even when it’s slower.

Third, group identity. Teams bond over shared work, and outside ideas can feel like a quiet challenge to the group’s sense of itself. Rejecting them protects the tribe.

A 2019 study led by Julian Hannen, again with Antons and Piller, put a number on the cost. Across the R&D professionals they surveyed, every one-point increase in Not Invented Here attitude corresponded to roughly a six percent decrease in how much external knowledge actually got absorbed. Small attitude shifts, measurable losses.

One more thing. The bias has a defense. In 2001, software developer Joel Spolsky wrote a widely shared essay arguing that strong teams should build their core stuff themselves, because nobody else’s work meets their bar. He wasn’t entirely wrong. Sometimes building it in-house is the right call.

The problem is when the source decides the answer before the evaluation happens.

Nobody in a meeting says, “I reject this because we didn’t make it.” People tend to say, “That doesn’t fit our context,” or “We already tried something like that,” or “Our users are different.” And sure, sometimes those statements are true. The bias is what happens when that is the first reaction rather than any real finding.

On product teams, the clearest version shows up between disciplines. An engineer suggests a UX change and design dismisses it before looking closely, because usability isn’t their lane. A designer proposes a technical approach and engineering does the same. The boundary that makes the idea feel external isn’t a company wall. It’s a job title.

Research gets hit hard by this. A team commissions a study from an outside agency, and when the findings contradict the team’s assumptions, the methodology suddenly looks questionable. Meanwhile, a hallway conversation with one internal stakeholder gets treated as solid evidence. The difference isn’t rigor. The agency’s work came from outside.

Design systems are a running battleground. A platform team ships a component. A product squad rebuilds nearly the same thing because the shared version “doesn’t quite work for us.” Multiply that across ten squads, and you have ten date pickers, ten sets of bugs, and a design system nobody trusts.

Engineering has its own famous version: rewriting a library instead of adopting one. Sometimes the rewrite is justified. Often it’s a year of effort to reproduce something that already existed, with fewer tests.

Product managers do it with competitor patterns. A rival ships a flow that clearly works, and the PM’s instinct is to differentiate rather than learn. Users don’t reward originality for its own sake. They reward things that work.

Then there’s the acquired team. A company buys a startup, and within months the parent company replaces the startup’s codebase, research, and product instincts with its own. The purchase price bought the knowledge. Not Invented Here throws it away.

The cost isn’t just wasted effort. It’s what Katz and Allen actually measured: teams that stop taking in outside information get worse over time, and they don’t notice because the feedback that would tell them has been filtered out.

There’s also a flip side worth using. This bias can work for you if you understand it. If you need a team to adopt an outside idea, hand it to them early and let them shape it. The moment they’ve adapted it, it stops feeling external. Some companies have flipped the phrase entirely and talk about ideas as “proudly found elsewhere.” Same bias, pointed in a useful direction.

The goal isn’t to distrust your own team’s work. It’s to notice when the source of an idea is doing the evaluating instead of you.