although he is an honest and strong man, John proctor has an Achilles heel--his relationship with abigal

The allusion shows that John's weakness was his affair with Abigail, thus bringing his relationship with Elizabeth (his wife) to a downfall as it seemed.

Explanation:

This would also foreshadow John Proctor's demise because of the affair. Achilles heel is Greek mythology, Achilles was invincible besides his heel. He eventually got shot in his heel, which caused his downfall.