The Art of War is one of the oldest and most successful books on military strategy. It has had an influence on Eastern military thinking, business tactics, and beyond. Sun Tzu suggested the importance of positioning in strategy and that position is affected both by objective conditions in the physical environment and the subjective opinions of competitive actors in that environment. He thought that strategy was not planning in the sense of working through an established list, but rather that it requires quick and appropriate responses to changing conditions. Planning works in a controlled environment, but in a changing environment, competing plans collide, creating unexpected situations.