In terms of databases, is “Normalize for correctness, denormalize for performance” a right mantra?

The two most common reasons to denormalize are:

1. Performance
2. Ignorance

The former should be verified with profiling, while the latter should be corrected with a rolled-up newspaper 😉

I would say a better mantra would be “normalize for correctness, denormalize for speed – and only when necessary”