Jutland's missed German night-fighting opportunity

Which mistake by one side created the greatest opportunity for another naval power?

Britain's weak First World War night-fighting doctrine gave Germany a major opportunity during the night phase at Jutland.

The British had to be cautious because friendly ships were numerous and difficult to identify in darkness. Their lack of a coherent night-fighting drill compounded that recognition problem and limited aggressive action. German forces, while escaping, could assume contacts were more likely British and might have exploited that asymmetry with greater aggression. Heavier British losses could have altered the wider war, making this a missed operational opportunity with strategic consequences.