The altar fire by A.C. Benson

One of the hardest things to face in the world is the grim fact that our power of self-improvement is limited. Of some qualities we do not even possess the germs. Some qualities we have in minute quantities, but hardly capable of development; some few qualities we possess in fuller measure, and they are capable of development; but even so, our total capacity of growth is limited, conditioned by our vital energy, and we have to face the fact that if we develop one set of qualities we must neglect another set.

I think of it in a whimsical and fantastic image, the best I can find. Imagine a box in which there are a number of objects like puff-balls, each with a certain life of its own, half-filling the box. Some of the puff-balls are small, hard, sterile; others are soft and expansive; some grow quickly in warmth and light, others fare better in cold and darkness. The process of growth begins: some of them increase in size and press themselves into every crevice, enclosing and enfolding the others; even so the growth of the whole mass is conditioned by the size of the box, and when the box is full, the power of increase is at an end.