In the final paragraph of his book titled The Conquest of Happiness, Bertrand Russell writes that
the whole antithesis between self and the rest of the world, which is implied in the doctrine of self-denial, disappears as soon as we have any genuine interest in persons or things outside ourselves. Through such interests a man comes to feel himself part of the stream of life, not a hard separate entity like a billiard-ball, which can have no relation with other such entities except that of collision.
Russell’s “billiard ball” simile is effective for a number of reasons, including the following:
- a billiard ball, by definition, has no feelings and has no association with life. It is dead matter. A stream, at least, can contain life, such as fish, plants, and other living things.
- a billiard ball, unlike a stream, seems small, self-contained, and relatively insignificant in the grand scheme of things. In contrast, a stream can be quite long and/or large and can play a significant role in nourishing not only the life it contains but also the life that grows along its banks.
- a billiard ball, once set in motion, will move in a completely predictable and rigid way until it does indeed collide with something else. It will then move instantly away from the object with which it collides. Thus, any contact between the ball and the object it hits will be extremely brief and will usually leave both entities completely unchanged except in their motion(s). In contrast, the path of a stream is never completely predictable; in fact, as a stream follows its path it often subtly alters that path, through such processes as erosion, flooding, etc.
- a billiard ball does not change. Once it has been created, it generally retains its original shape, mass, weight, etc., until something alters or destroys it. In contrast, a stream is constantly in the process of changing, evolving, growing, shrinking, etc.
For all these reasons and others, Russell’s “billiard ball simile” seems an effective one.