From “The Sick Soul” by William James, part of The Varieties of Religious Experience:

Recent psychology has found great use for the word ‘threshold’ as a symbolic designation for the point at which one state of mind passes into another. Thus we speak of the threshold of a man’s consciousness in general, to indicate the amount of noise, pressure, or other outer stimulus which it takes to arouse his attention at all. One with a high threshold will doze through an amount of racket by which one with a low threshold would be immediately waked. Similarly, when one is sensitive to small differences in any order of sensation we say he has a low ‘difference-threshold’—his mind easily steps over it into the consciousness of the differences in question. And just so we might speak of a ‘pain-threshold,’ a ‘fear-threshold,’ a ‘misery-threshold,’ and find it quickly overpassed by the consciousness of some individuals, but lying too high in others to be often reached by their consciousness. The sanguine and healthy-minded live habitually on the sunny side of their misery-line, the depressed and melancholy live beyond it, in darkness and apprehension. There are men who seem to have started in life with a bottle or two of champagne inscribed to their credit; whilst others seem to have been born close to the pain-threshold, which the slightest irritants fatally send them over.

Does it not appear as if one who lived more habitually on one side of the pain-threshold might need a different sort of religion from one who habitually lived on the other? This question, of the relativity of different types of religion to different types of need, arises naturally at this point, and will become a serious problem ere we have done. But before we confront it in general terms, we must address ourselves to the unpleasant task of hearing what the sick souls, as we may call them in contrast to the healthy-minded, have to say of the secrets of their prison-house, their own peculiar form of consciousness. Let us then resolutely turn our backs on the once-born and their sky-blue optimistic gospel; let us not simply cry out, in spite of all appearances, “Hurrah for the Universe!— God’s in his Heaven, all’s right with the world.” Let us see rather whether pity, pain, and fear, and the sentiment of human helplessness may not open a profounder view and put into our hands a more complicated key to the meaning of the situation.