If there is one secret of effectiveness, it is concentration. Effective executives do first things first and they do one thing at a time.
Doing one thing at a time means doing it fast. The more one can concentrate time, effort, and resources, the greater the number and diversity of tasks on can actually perform.
This is the secret of those people who “do so many things” and apparently so many difficult things. They do only one at a time. As a result, the need much less time in the end than the rest of us.
Concentration - that is, the courage to impose on time and events in his own decision as to what really matters and comes first — is the executive’s only hope of becoming the master of time and events instead of their whipping boy.
Drucker, P. (1967). The Effective Executive: The Definitive Guide to Getting the Right Things Done. Harper-Collins.
The art of management lies in the capacity to select from the many activities of seemingly comparable significance the one or two or three that provide leverage well beyond the others and concentrate on them.
Grove, A. (2015). High Output Management. Vintage.