The hysteria that permeates the town of Salem and the surrounding environs in Arthur Miller's play The Crucible, a story intended as an allegory for the "witch hunts" that took place in the United States during the late 1940s and early 1950s when fears of communism and the Soviet Union gripped much of the nation, causes the region's inhabitants to act irrationally and viciously towards each other. Friends turn on friends; family members turn on family members. Fear of being accused of sorcery is sufficient to cause people to make ill-founded accusations in order to deflect suspicions away from themselves. Such is the atmosphere in which Miller's play takes place. From its opening scene, in which Reverend Parris frantically tries to deal with his daughter's apparent coma following her and her friends' peculiar and highly suspicious activities in the woods, The Crucible depicts a society on the threshold of a Hell of its own making.
As Miller's play progresses, the hysteria reaches a fever pitch, and old grievances become the fodder for new ones, all intended to ensure one's survival. At the center of this drama are Abigail, whose actions precipitate the tragic chain of events, and, increasingly, Mary Warren, Abigail's replacement in the Proctor home following Abigail's dismissal for engaging in sexual relations with John Proctor. Proctor's relationship to Abigail continues to plague him, and he becomes dependent upon Mary's testimony in court to absolve him while indicting Mary's friend, Abigail. Mary knows of Proctor and Abigail's affair, and is caught between her employer and her friend. As Miller depicts the scene late in Act Two:
Mary Warren: . . .Abby'll charge lechery on you, Mr. Proctor!
Proctor: She's [Abigail] told you!
Mary Warren: I have known it, sir. She'll ruin you with it, I know she will.
Proctor is desperate to ensure Mary's testimony will exonerate him in the witch trial that is tearing the town apart. In Act Three, Proctor testifies before the court that Mary is prepared to confess that charges of sorcery, or witchcraft, have been fabricated, and that her previous statements were false. As Mary is questioned by Danforth, however, Abigail and the other girls enter the court room. Danforth questions Abigail regarding Mary's deposition and testimony, and Abigail accuses her now-former friend of lying when Mary denies any kind of Satanic activities. Abigail succeeds in turning the tables on Mary and, by extension, John Proctor. Abigail pretends to be experiencing symptoms of demonic influence, which casts new suspicions upon Mary, who is now, again, suspected of sorcery. Abigail, as we know from the play's previous activities, is far more duplicitous in nature than the more simple-minded Mary Warren, and the latter breaks down, lending credence to Abigail's intrigues.
In short, Mary is sufficiently frightened by Abigail's tactics that her fear overshadows any commitments she has made with Proctor.
As noted, Miller intended his play as an allegory about the anti-communist paranoia that permeated the nation during the early 1950s. The point he makes in The Crucible, especially during the trials, is that innocent people suffered unjustly because of the paranoia about threats that did not, or only marginally, existed. Honest people felt compelled to accuse others in order to deflect attention away from themselves.