Tapeworms
They drain all the nutrients out of their host, leaving precious little for him/her/it. That's why people and animals with tapeworms are so unhealthily thin.
I seriously think that, on the metaphysical front, there are mental and philosophical tapeworms that drain all the emotional energy and love for life out of you. The result is an unhappy and unfulfilled person. Like the real tapeworm, thoughts and philosophies like this only exist for themselves and do not benefit you. In many cases, holding them doesn't even benefit other people.
I seriously think that, on the metaphysical front, there are mental and philosophical tapeworms that drain all the emotional energy and love for life out of you. The result is an unhappy and unfulfilled person. Like the real tapeworm, thoughts and philosophies like this only exist for themselves and do not benefit you. In many cases, holding them doesn't even benefit other people.