Have you thought about the consequences of using a library?

This won’t take weeks, I know a library that can do this. I’ll have it implemented by tomorrow.

It’s a familiar line. Engineers say it often, especially when speaking to founders looking for speed. It’s appealing: efficient, pragmatic, and backed by the logic that there’s no need to reinvent the wheel if a solution exists.

What’s happening here is a smaller-scale version of the classic build-versus-buy decision. Non-technical founders are particularly drawn to it. Stories of how other startups implemented a feature in a day by dropping in a ready-made library or component often influence them. However, these stories tend to gloss over reality: integrating a library is only the beginning. Every library brings trade-offs, and treating it as a silver bullet can create more problems than it solves.

Let’s say the chosen library is a good one. It might cover 80 to 95 percent of what the product needs. The crucial question becomes: what happens with the remaining 5 percent? Too often, that part of the conversation doesn’t happen. Engineers want to be seen as solution-oriented and fast-moving. Interested to move forward, founders might dismiss the edge cases as minor details.

Until they’re not.

Sooner or later, a major client needs the functionality that wasn’t included. Founders, having assumed the library covered everything, are surprised. Engineers, now committed to the integration, are bending a closed system into shapes it wasn’t designed for. That last 5 percent becomes a drain on time and focus, a patchwork of hacks and workarounds, and the original estimate of “a day’s work” turns into a recurring problem with no clean resolution.

These decisions seem straightforward in the moment. But before reaching for the quick fix, it’s worth pausing. What doesn’t the library support? Is that missing piece truly optional, or just misunderstood? Can we live without it? Or are we creating technical debt that will come due at the worst possible time?

What looks like a shortcut today can easily become tomorrow’s limitation.