The excerpt describes the breakdown of unity among a group that is isolated, such as shipwreck survivors or those under siege. It highlights how feelings of jealousy and dissent begin to emerge, creating a rift in their collective mindset. These negative emotions can lead to conflict, as the group's cohesion deteriorates under pressure, allowing for a darker side to surface which distracts them from external threats.

As tensions heighten, an external adversary arrives, representing not just an outside danger but also a culmination of their internal struggles. The inability to maintain harmony and the preoccupation with individual grievances allow this "foe" to enter their lives. This scenario illustrates how internal conflicts can open the door to external dangers, emphasizing the fragility of solidarity when confronted with adversity.