A new employee should receive the unwritten rules before being judged for breaking them.

Every workplace runs on conventions nobody wrote down: how early counts as late, which meetings are real, whether a Friday deadline means Friday or Monday morning. New people get assessed against those rules before anyone confirms the rules exist, and the assessment tends to outlast the mistake by a long way.

If someone joined recently, tell them one unwritten rule this week without being asked. If you manage anyone, hold your conclusions for a month and say so out loud.