[selfhoster11]

Your manager is always potentially your adversary: after all, they can fire you if they are unhappy with what they are seeing.

Not to mention that some managers simply are adversarial, period. When you apply to a company, you can rarely choose your manager, and sometimes cannot work under a different manager without leaving the company entirely.

[Gareth321]

I've had adversarial managers in the past. Unsurprisingly, the team underperformed and the culture was terrible, so I left. I don't agree that one's manager should be one's adversary. I've worked with many managers who work with me instead of against me. This is a crucial difference.