When you leave your house, concentrate your mind on a subject (no matter what, to begin with). You will not have gone ten yards before your mind has skipped away under your very eyes and is larking round the corner with another subject. Bring it back by the scruff of the neck. Ere you have reached the station you will have brought it back about forty times. Do not despair. Continue. Keep it up. You will succeed. You cannot by any chance fail if you persevere.
