Every time this happens, Amazon crushes another legacy retail sector

``When online sales hit 20% of all purchases in a given retail category, a surge in Amazon growth is sure to follow, according to L2 Inc., a business intelligence firm. It's a threshold indicating "Amazon is going to displace a legacy retailer," said Cooper Smith, L2's director of Amazon research. "Twenty percent is when Amazon steps on the gas ... when consumer behavior is changing."''