Often when works at a hard question, nothing good is accomplished at the first attack. Then one takes a rest, long or short, and sits down anew to the work. During the first half-hour, as before, nothing is found, and then all of a sudden the decisive idea presents itself to the mind.
Henri PoincareIf nature were not beautiful, it would not be worth knowing, and if nature were not worth knowing, life would not be worth living
Henri Poincare