I think the article captures the problem even better than a similar one that was recently on the frontpage of HN: https://news.ycombinator.com/item?id=17850836

I can't remember a situation where undergeneralized code came back to bite me. I have however seen (and admittedly written some) prematurely generalized code that became messy legacy code.

You often can't tell up-front. If you never get back more than what you put into an abstraction, it was probably over-engineered.