T 2.3.5.4

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 thro' custom; but such as are naturally attended with some emotion or affection, which is destroy'd by the too frequent repetition. One can consider the clouds, and heavens, and trees, and stones, however frequently repeated, without ever |feeling any aversion. But when the fair sex, or music, or good cheer, or any thing, that naturally ought to be agreeable, becomes indifferent, it easily produces the opposite affection.