Reorganising in the first month
Changing rituals, scopes or tools before understanding why they exist produces lasting rejection. Every rule in place was written by an incident; until you know the incident, you are deleting an answer without knowing the question.
Criticising your predecessor, even mildly
Any dig at the previous manager attacks, by ricochet, eight years of the team’s work with him. You place yourself on one side of a line and stay there. Visible respect for what came before is the entry condition, not a courtesy.
Trying to be adopted
Multiplying friendly gestures and avoiding every unpopular decision for three months reads as weakness and extends the testing period instead of closing it. A hostile team is testing solidity, not likeability.
Treating challenge as a discipline problem
Calling in your most critical team member for a formal correction in week three makes them a martyr and unites everyone else against you. That person is usually the best-informed member of the team: a resource before they are an obstacle.
Waiting for time to do the work
Without a concrete demonstration, the testing period does not fade — it settles in. After three or four months the team has reached its conclusion, and reopening the file costs far more than dealing with it early.