Everything "potentially leads" to adverse outcomes if not applied with due care and cognizance. That includes KISS and YAGNI. If you're looking for a principle you can apply in 100% of cases without consideration of context, I'm afraid you'll need to shop elsewhere.

> if not applied with due care and cognizance

That's the gotcha though. Everything applied with due care and cognizance works. This is not what is being discussed here. What the author suggests does lead to overengineering though. Think of stereotypical enterprise Java code if you need examples

The context was "business", that kind of application is developed quite differently than, say, a cool little hobby terminal emulator or whatever.

Even though the business currently doesn't have a need to e.g. support any other currency than USD and EUR, an experienced developer will clearly see that it is unlikely to stay that way for long, so doing some preliminary preparation for generalizing currencies may well worth the time.

>Even though the business currently doesn't have a need to e.g. support any other currency than USD and EUR

Your regular business requirements are way more complex than just a currency list. This is like trying to justify your point using an oversimplified example imo.