It ruined my friend's startup. Junior dev "wrote" WAY too much code with no ability to support it after the fact. Glitches in production would result in the kid disappearing for weeks at a time because he had no idea how anything actually worked under the hood. Friend was _so_ confident of his codebase before shit hit the fan - the junior dev misrepresented the state of the world, b/c he simply didn't know what he didn't know.