Changing circumstances and ongoing managerial efforts to improve the strategy account for why a company's strategy evolves over time and why the task of crafting a company's strategy is a work in progress, not a one-time event. explain why a company's sales and profits are always going up or down. make it very hard to know what a company's strategy really is. make it very difficult for a company to achieve a sustainable competitive advantage. create conditions where a company's business model is always changing.