There is nothing more dreadful than the habit of doubt. Doubt separates people. It is a poison that disintegrates friendships and breaks up pleasant relations. It is a thorn that irritates and hurts; it is a sword that kills.
The answer to old age is to keep one's mind busy and to go on with one's life as if it were interminable. I always admired Chekhov for building a new house when he was dying of tuberculosis.