In The Crucible, what is Mary Warren's motivating factor & how does it positively/negatively affect herself & other characters in the play?I am...

Mary Warren is primarily motivated by the same factors
that motivated so many of the others at that time in Salem, Massachusetts - fear and
ignorance.  Mary was afraid of Abby and of being accused of witchcraft herself.  Like
the other girls who pointed fingers of accusation at people, Mary was caught up in the
frenzy.  When the girls are caught by Rev. Parris in the woods playing with white magic,
they are all afraid of what punishments will come to them.  As soon as they start crying
"Witch!" and see that they now become victims instead of perpetrators, they all start
using that ploy.  Abby is the ring leader in the play, telling the girls in Act 1 that
they need to stick to their story and she threatens violence on any girl that goes
against her.  Apparently the girls do not doubt Abby's capacity for violence because
they heed what she says even though Mary Warren has suggested that they all just admit
to dancing and take their whipping for that misdeed rather than lie about what went on. 
Later, when Mary brings the poppet to Elizabeth, it seems that she has simply been
keeping her hands busy as she sat in court all day - that she had no ulterior motive in
making the little doll.  When Mary goes to court in Act 3 to confess that the girls lied
about the allegations of witchcraft, Abby turns against her because Mary's claim makes
Abby out a liar.  Abby starts to say that Mary is a witch and out of fear, Mary recants
and says that John Proctor made her say she and the other girls lied about being
tormented by witches.  Mary is very afraid of Abby and what Abby might do to her.  She
knows that if Abby accuses her of witchcraft, and the other girls follow her as they are
doing, that she will go to prison and possibly be hanged.  The ignorance comes to play
because the people did believe that witches could be among them and that hanging those
accused by girls was the right action to take.