Most code is written to be replaced. A small fraction is written to last. The difference isn't talent—it's intention. Over the last ten years, I've seen frameworks rise and fall, paradigms shift from object-oriented to functional and back again, yet some parts of our system remain untouched, performing their duties as reliably as the day they were committed.
Boring is a Feature
The codebases I've watched survive a decade share one trait: they are aggressively boring. They don't use the latest experimental features. They don't rely on clever "magic" that saves three lines of code at the cost of two hours of debugging. They use the framework's defaults and follow established patterns.
Code is read far more often than it is written. Optimize for the reader of the future, who is likely you, six months from now, and very confused.
The Truth About Technical Debt
We often talk about technical debt as if it's something we can just pay off with a big refactor. But the reality is more like a mortgage. You live with it, you manage it, and you make sure it doesn't get so high that you can't afford the interest. The best engineers aren't those who write "perfect" code, but those who know which corners are safe to cut today and which will lead to a collapse tomorrow.
Tests as the Only Documentation That Matters
A test suite is the most honest documentation a project can have. It can't lie because it runs. If a function's behavior changes, the test fails. If the test passes, the behavior is as specified. In a decade-old codebase, the tests are the only reason we have the confidence to change anything at all.