The most difficult job in an agency is Chief Executive Officer. He (or she) must be a good leader of frightened people. He must have financial acumen, administrative skill, thrust, and the courage to fire non-performers. He must be a good salesman, because he is responsible for bringing in new clients. He must be resilient in adversity. Above all, he must have the physical stamina to work 12 hours a day, dine out several times a week, and spend half his time in airplanes.

David Ogilvy. Ogilvy on Advertising.

Вот оно слово — stamina! Конечно, Огилви пишет про рекламное агенство, но его слова наверно подойдут к любому бизнесу.