YAGNI is not about things you know you need, because then you wouldn’t write any code ever.

This was the issue with the early agile-developed systems.

Not that they didn’t write no code, obviously, but they didn’t understand the domain and so YAGNI’d everyone to death. As a result there wasn’t enough code for the system would do what it needed to do.

The code was simple and highly testable, but didn’t actually do the job.