I'd contend you only know something if it's contained within a very rigid and small box that you can easily hold within your mind. Like, I can learn all about a

I'd contend you only know something if it's contained within a very rigid and small box that you can easily hold within your mind. Like, I can learn all about a sample dataset, but my real-world SQL data sources are vastly dirty and have tons of edge-cases I learn about from week to week. For 99.9999% of things, there is simply too much depth and breadth to ever hold that information-box in your mind.