Whenever the new thinking, however weak and anemic, becomes the common thinking, the mind becomes quick to lock out the old thinking as “impossible” or “not practical or desirable.”

Look at a stone cutter hammering away at his rock, perhaps a hundred times without as much as a crack showing in it. Yet at the hundred-and-first blow it will split in two, and I know it was not the last blow that did it, but all that had gone before.