A proverb meaning there is no rule without exceptions; every rule has its exceptions.
理論は正しいが、実践では例外のない規則はないと考えた方がいい。
The theory is correct, but in practice it's better to assume that every rule has exceptions.
例外の無い規則は無いということを忘れて、厳格に運用すると問題が起きることがある。
Forgetting that there are no rules without exceptions and applying them rigidly can cause problems.
この業界でも例外のない規則はないので、柔軟な対応が必要だ。
Even in this industry there are no rules without exceptions, so flexible handling is necessary.