Or, as a wise man once said, "Premature optimization is the root of all evil."

It's a different part of the field of course, but so many people yield opportunity cost chasing some difficult architectural problem that will likely never impact you, and if it does you'll have resources to throw at it.

Many startups won't even have slave production databases, much less have to worry about network distributed sharding, complex caching strategies, database optimization beyond query analysis.