He must concentrate _all his energies_ upon the one thing.

If worry occupies his attention, wit, sense, judgment, discretion, wisdom are crowded out, have no place.
All the pictures given to us of Grant show him the most imperturbable at the most trying times.

When the fortunes of war seemed most against him he was the most cheerful, the least disturbed.

He had learned the danger of worry, and compelled it to flee from him, that calm judgment and clear-headed decisions might be his.
If, therefore, these great ones of earth found it essential to their well-being to banish worry, how much more is it necessary that we of the ordinary mass of mankind, of the commoner herd, apply ourselves to the gaining of the same kind of wisdom.
An old countrywoman once said in my hearing: "Worry, and you hug a hornet's nest." How suggestive both of the stinging that was sure to come and the folly, the absurdity, the cruelty to oneself of the act.
The great Scotch philosopher, Blair, said: "Worry (or anxiety) is the poison of human life," and how true it is.

How biting, how corroding, how destructive to life some poisons are, working speedily, suddenly, awfully.