Technical debt is known as "deferred maintenance" in real estate. If you don't update your tools / legacy software / hardware then you will run into a failure sooner than later. Addressing debt can also introduce failures but that at least has a fall-back solution [roll back the refactoring]. Basically software written years ago is rarely of a quality that it could be "left alone" without any fixes for unforeseen requirements [i.e. does your 20 year old software handle emoji?]