2-79. The decisive operation is the operation that directly accomplishes the mission (ADP 3-0). Weighting the decisive operation or the main effort is a basic tactical concept closely associated with the mass and maneuver principles of war. The purpose for weighting the decisive operation or main effort is to concentrate the effects of combat power at the most advantageous place and time. A unit commander assumes risk in some areas to provide the resources required to mass combat power at a few key locations to support the unit’s decisive operation or main effort.