Leaders are Human But...
While we like to think human beings act consistently, you'd be surprised at how inconsistent people are, primarily because our behavior is heavily influenced by the context and situation. That's normal and people around us actually tolerate a lot of inconsistencies (although they tend to tolerate it for themselves, but less for others).
Leaders need to be at least somewhat consistent and predictable in their approaches to things, while remaining adaptable and flexible. That's because trust, a central aspect of effective leadership, has, as one of its components, predictability. A follower cannot trust a leader who, one day is pleasant and helpful, and on another day abusive and nasty. Or who, one day makes decisions according to one set of criteria, then the next applies a completely different set to a similar situation.
Leadership Errors - Behaving Inconsistently