GRAMMAR DETAIL

〜ならいざ知らず

perhaps if it were · would be one thing, but

First names a condition that could be accepted as an exception, then contrasts it with the present case, which does not qualify.

Examples

初めてならいざ知らず、同じ失敗を三度も繰り返すのは問題だ。

If it were the first time, that would be one thing, but repeating the same mistake three times is a problem.

初心者ならいざ知らず、経験者が同じミスをするのは不思議だ。

A beginner making the mistake would be one thing, but it is strange for an experienced person to make the same error.

Structure: Attach ならいざ知らず to a condition that might be accepted as an exception, contrasting it with a present case that does not qualify.
Basic usage: 初めてならいざ知らず、同じ失敗を三度も繰り返すのは問題だ。 judges repeating the same mistake three times difficult to excuse, unlike a first mistake.

Contrast after naming an exception
- 初心者ならいざ知らず sets a beginner's case aside as a possible exception. The contrast with 経験者が同じミスをする presents the same mistake as unexpected from an experienced person.