The development of the mind is immediately disturbed by the inactivity of the same, for the mind is a force that can be developed only by exercise; or it is disturbed by too great an exertion, accompanied by neglect of the body that has to support it; or it is disturbed by the mind's own disorderly activity, or by the blind enthusing of the imagination, without aim or rule, or by learning alien thoughts purely by rote and without exercising one's own judgment, or by sterile brooding unaccompanied by any living intuition.