A rival has almost as close a relation to me as a partner.

For as the pleasure of the latter causes my pleasure, and his pain my pain; so the pleasure of the former causes my pain, and his pain my pleasure.

The connexion, then, of cause and effect is the same in both cases; and if in the one case, the cause and effect have a farther relation of resemblance, they have that of contrariety in the other; which, being also a species of resemblance, leaves the matter pretty equal.
The only explication, then, we can give of this phaenomenon is derived from that principle of a parallel direction above-mentioned.

Our concern for our own interest gives us a pleasure in the pleasure, and a pain in the pain of a partner, after the same manner as by sympathy we feel a sensation correspondent to those, which appear in any person, who is present with us.

On the other hand, the same concern for our interest makes us feel a pain in the pleasure, and a pleasure in the pain of a rival; and in short the same contrariety of sentiments as arises from comparison and malice.