If they mess up the delivery system, then they will end up as a brick and mortar store and they'll become the next Sears.
It took Sears from 1893 until present to more/less totally fail. Along the way they were involved with Allstate Insur, Coldwell Banker real estate, to name examples of "conglomerate" businesses.
Amazon started in 1994 and is now almost beyondcomprehension.
They too are bound to make mistakes.
But the world of business moves very fast now. Amazon and Walmart seem to be competing for the grand kahuna of retail, online and neighborhood.
My business mind says no seller can make a profit selling $5 items, and providing overnight delivery to households.
It is very difficult to argue that Amazon lacks highly agile smart management.
I remember when the first Starbucks came to my area--also 1994.
It was sort of cultural arrival. We had been deemed to be sufficiently cool, to "get" a Starbucks. Now there are 6 to 8 within a couple of miles. They are starting to upgrade, replace locations with better ones.
Speed, risk, decisiveness seem to be aspects of these business "replication" and "scaling" examples.
I expect Amazon, Starbucks and Walmart will linger as long as Sears did, over mistakes.