A foolish enemy will assume you will attack only directly. If they are less foolish, you can still keep them on their toes with regular indirect attacks such that they have to distribute their troops everywhere.
If you are good at defending, you can hold off a larger force which remains puzzled as to what attacks to use and so does not attack.
Ways to do this include taking superior positions and having good intelligence and mobile troops who can reach defensive positions before the enemy arrives.
This principle is equally applicable in business. If you can take market share and defend your own, you will grow and grow.