Why Do Some Messy Codebases Remain Surprisingly Stable?

“Shit mountain” code can remain stable like an old house that survives storms, despite its messy appearance.

This stability is the result of accumulated technical debt; over time the code adapts, many bugs are hidden, and the system survives because unstable versions are discarded.

Contributors note that such code persists because it is continuously maintained by many developers, and because rigorous testing and processes can make even low‑quality code function reliably.

Testing‑driven development is highlighted as a key factor: extensive automated tests allow even legacy code to be trusted, and code reviews focus on test quality rather than aesthetic elegance.

Example of test‑driven development shows a simple

isPrime

function evolving through iterations to handle more cases as tests reveal failures.

<code>bool isPrime(int nNumber) {
    return false;
}
</code>

<code>bool isPrime(int nNumber) {
    if (nNumber == 3) return true;
    if (nNumber == 5) return true;
    return false;
}
</code>

When enough time is spent testing and refining, the code becomes stable, but adding new features or refactoring can quickly expose its fragility.