As they get bigger, most legacy companies find they have long lost the initial speed, agility, and vitality commonly found in start-ups. They have become rigid, slow, and risk-averse; complacency and bureaucracy have crept in. Some could sustain for a while, some would gradually fall into oblivion or irrelevance, some would become the prey for aggressive acquirers, and only a few could continuously refresh themselves.
Amazon, as an organization, is committed to be Forever Day-1, that is, to combine the size and scale advantages of a big company, the speed and agility of a startup, and the continuous upgrade of organizational capabilities.