Do you know, I always thought unicorns were fabulous monsters, too? I never saw one alive before!" Well, now that we have seen each other," said the unicorn, "if you'll believe in me, I'll believe in you.
My hand moves because certain forces--electric, magnetic, or whatever 'nerve-force' may prove to be--are impressed on it by my brain. This nerve-force, stored in the brain, would probably be traceable, if Science were complete, to chemical forces supplied to the brain by the blood, and ultimately derived from the food I eat and the air I breathe.
When I come upon anything-in Logic or in any other hard subject-that entirely puzzles me, I find it a capital plan to talk it over, aloud, even when I am all alone. One can explain things so clearly to one's self! And then, you know, one is so patient with one's self: one never gets irritated at one's own stupidity!
When you have made a thorough and reasonably long effort, to understand a thing, and still feel puzzled by it, stop, you will only hurt yourself by going on.