When planning an action, one must allocate more than sufficient resources to help insure success. Concentrate or mass resources to execute actions quickly and effectively.

MASS means concentrate combat power at the decisive place and time. More generally the principle is concentrate your efforts, don't scatter your forces.

ECONOMY OF FORCE means allocate minimum essential combat power to secondary efforts.

The priciples of MASS and ECONOMY OF FORCE are two of 9 Principles of War in the Army Field Manual (FM-3) of Military Operations.

from Army Field Manual (FM-3) of Military Operations
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