I have always hesitated to give advice, for how can one advise another how to act unless one knows that other as well as one knows himself? Heaven knows. I know little enough of myself: I know nothing of others. We can only guess at the thoughts and emotions of our neighbours. Each one of us is a prisoner in a solitary tower and he communicates with the other prisoners, who form mankind, by conventional signs that have not quite the same meaning for them as for himself.