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.
By degrees the repetition produces a facility of the human mind, and an infallible source of pleasure, where the facility goes not beyond a certain degree.

And here it is remarkable that the pleasure, which arises from a moderate facility, has not the same tendency with that which arises from novelty, to augment the painful, as well as the agreeable affections.

The pleasure of facility does not so much consist in any ferment of the spirits, as in their orderly motion; which will sometimes be so powerful as even to convert pain into pleasure, and give us a relish in time what at first was most harsh and disagreeable.
But again, as facility converts pain into pleasure, so it often converts pleasure into pain, when it is too great, and renders the actions of the mind so faint and languid, that they are no longer able to interest and support it.

And indeed, scarce any other objects become disagreeable through custom; but such as are naturally attended with some emotion or affection, which is destroyed by the too frequent repetition.