Relational database queries are supposed to be _declarative_. As a user, you're not supposed to think about the mechanics of execution because the database system is supposed to be able to decide how to execute your query using whatever magic it wants, as long as it satisfies the contract that it gives you the right answer.

It's absolutely useful as a debugging tool to build up some semantic understanding of what the query means, and I encourage every database user to learn to use EXPLAIN, but relying on a mental execution model is borderline dangerous.