Parent is talking about beautiful schema, not a beautiful query planner. If you are capable of understanding the concept of abstraction and encapsulation, you can design a good system knowing the performance characteristics of your components but not their internals.
The geniuses who wrote postgres don't know how to write responsive web sites. The geniuses who make gorgeous fast websites don't know how a Btree is implemented. It's OK. That's how the global economy works.
But the fast-website people still need to know what makes a query slow and how to improve it. They don't (and shouldn't) write their own database engine, but they need to know how their equipment works.
The geniuses who wrote postgres don't know how to write responsive web sites. The geniuses who make gorgeous fast websites don't know how a Btree is implemented. It's OK. That's how the global economy works.