Someone wrote me the other day, asking, "When is the best time to acquire knowledge?" I answer, "The time is now." It is easier to learn things when you are young, but you cannot be young when you want to be, and if you are old, the best time to acquire knowledge is when you are old. It is true that the brain-cells seem to harden like the body, and it is less easy for them to take on new impressions; but it can be done, and just as Seneca began to learn Greek at eighty, I know several old men whom the recent war has shaken out of their grooves of thought and compelled to deal with modern ideas. But if you are young, then so much the better! Then the divine thrill of curiosity is keenest; then your memory is fresh, and can be trained; your mind is plastic, and you can form sound habits. You can teach yourself to respect truth and to seek it, you can teach yourself accuracy, open-mindedness, flexibility, persistence in the search for understanding. First of all, I think, is accuracy. Learn to think straight! Let your mind be as a sharp scalpel, penetrating unrealities and falsehoods, cutting its way to the facts. When you set out to deal with a certain subject, acquire mastery of it, so that you can say, "I know." And yet, never be too sure that you know! Never be so sure, that you are not willing to consider new facts, and to change your way of thinking if it should be necessary. I look about me at the world, and see tigers and serpents, dynamite and poison gas and forty-two centimeter shells--yet I see nothing in the world so deadly to men as an error of the mind. Look at the mental follies about you! Look at the prejudices, the delusions, the lies deliberately maintained--and realize the waste of it all, the pity of it all!