The tool may malfunction. Indeed there are theorems that say the tool must malfunction at least sometimes.

If you don't understand the subject and relies on the understanding of the tool, how will you have a frigging chance of catching an error?

Anyway this reminds me that scene in Matrix 2, where the mayor (of sorts, don't remember his exact title) of Zion tells Neo about the machines that keeps everyone alive, but that there is nobody left that understands how they work or could repair them if they broke.