No broken window maintains standard

Broken windows accelerates software entropy, therefore doing the opposite, where we have no broken, may encourages people to keep that state. People tend to give extra care as they don't want to be the person who breaks the window first.

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References

The Pragmatic Programmer (p. 8).

By the same token, if you find yourself on a project where the code is pristinely beautiful - cleanly written, well designed, and elegant - you will likely take extra special care not to mess it up, just like the firefighters.