The principle
Trouble can often be traced to a single strong individual — the stirrer, the arrogant underling, the poisoner of goodwill. Remove that one source and the surrounding problem dissolves with it.
The application
Most organisational dysfunction is upstream of a single person. Treat the symptom and you treat forever. Treat the cause and the room exhales.
The defensive tell — how to spot it being run on you
When a team starts unravelling shortly after one specific person joined, the pattern is real. The reorganisation, the reassignment, the polite exit — these are the leadership-level moves that prevent the unravel from spreading.