The man who cannot occasionally imagine events and conditions of existence that are contrary to the causal principle as he knows it will never enrich his science by the addition of a new idea.
Scientific work will never stop, and it would be terrible if it did. If there were no more problems, you would put your hands in your pockets and your head on a pillow and would work no more. In science rest is stagnation, rest is death.
We are in a position similar to that of a mountaineer who is wandering over uncharted spaces, and never knows whether behind the peak which he sees in front of him and which he tries to scale there may not be another peak still beyond and higher up.
