Once upon a time I had to track down a catastrophic performance failure (process that should have taken a few minutes couldn't finish in the THREE DAYS allotted

Once upon a time I had to track down a catastrophic performance failure (process that should have taken a few minutes couldn't finish in the THREE DAYS allotted to it as a maximum runtime) that turned out to be because it was using a hand-rolled "simple" JSON parser instead of just pulling in Newtonsoft.