A Treatise of Human Nature by David Hume — Read

But nothing has a greater effect both to encrease and diminish our passions, to convert pleasure into pain, and pain into pleasure, than custom and repetition. Custom has two original effects upon the mind, in bestowing a facility in the performance of any action or the conception of any object; and afterwards a tendency or inclination towards it; and from these we may account for all its other effects, however extraordinary.

When the soul applies itself to the performance of any action, or the conception of any object, to which it is not accustomed, there is a certain unpliableness in the faculties, and a difficulty of the spirit's moving in their new direction. As this difficulty excites the spirits, it is the source of wonder, surprize, and of all the emotions, which arise from novelty; and is in itself very agreeable, like every thing, which inlivens the mind to a moderate degree. But though surprize be agreeable in itself, yet as it puts the spirits in agitation, it not only augments our agreeable affections, but also our painful, according to the foregoing principle, that every emotion, which precedes or attends a passion, is easily converted into it. Hence every thing, that is new, is most affecting, and gives us either more pleasure or pain, than what, strictly speaking, naturally belongs to it. When it often returns upon us, the novelty wears off; the passions subside; the hurry of the spirits is over; and we survey the objects with greater tranquillity.