"We are all only mortal," said the Master, even more slowly. "We do only what we can do. All the Elemental priests have certain teachings in common: one of them is that everyone, every human, every bird, badger and salamander, every blade of grass and every acorn, is doing the best it can. This is the priests' definition of mortality: the circumstance of doing what one can is that of doing one's best. Only the immortals have the luxury of furlough. Doing one's best is hard work; we rely on our surroundings because we must; when our surroundings change, we stumble. If you are running as fast as you can, only a tiny roughness of the ground may make you fall." --