When you find PHP code that generates dynamic javascript

I don't always wreck the production environment, but when I do it's because I'm trying to refactor a piece of code with a "// this is here for reasons, don't change this" comment above it.

1) Writing data to database works just fine
2) Query reading back that same data returns null
3) Spend 3 hours to try figure out why that 4 year old select statement suddenly doesn't work anymore
4) Figure out mysql master stopped replicating to read slaves
5) Facepalm and cry a little