Millicent Bell says, "Contemporary records indicate that in the 1840s--the period in which 'The Turn of the Screw' seems to be set-- governesses accounted for the single largest category of female patients in English asylums for the insane." That is, whatever is troubling the young lady who tells us the story appears to be an occupational hazard. She has a lot of company.
We should look at the emotional state the governess is in just before the ghosts appear to her. Prior to seeing Peter Quint, she finds herself "under a charm," "lifted aloft on a great wave of infatuation and pity." She says her feeling is "actually like the spring of a beast" (!). She saunters along in the garden of Bly, and she loves it because "it was a pleasure at these moments to feel myself tranquil and justified; doubtless perhaps also to reflect that by my discretion, my quiet good sense and general high propriety, I was giving pleasure--if he ever thought of it!--to the person to whose pressure I had yielded." That "he," that "person," is, of course, her employer. She says, "Well, I needed to be remarkable." She wishes that "some one would appear there at the turn of a path and would stand before me and smile and approve. I didn't ask more than that--I only asked that he should know." And suddenly her "imagination had, in a flash, turned real. He did stand there!" But she fears what she wants; she instinctively knows that it is not right for her to engineer "the fine machin