A lot of startups' products are write-intensive applications with the following requirements:

- strong read-after-write consistency (or their users could receive inaccurate information)

- as-high-as-possible availability (because they lose money whenever the site goes down)

- low-latency operations that are difficult to optimize--such as recommendations, complex full-text search, or large graph traversal

And engineering teams don't notice that their solutions are suboptimal until their product hits scale.