You don't have to know anything, you can just pay somebody who does know. There was a time when that was the role of the audio dealer. Now people are into the "journey" and want to make their own choices. Some people quickly figure stuff out and others wander thru the desert. At some point it really doesn't matter because we're not designing commercial aircraft where mistakes can cost lives.
Is it possible to really know what you're doing?
Somehow I managed to select components that are getting along and feel comfortable with how things are sounding after many upgrades. I rely on others to advise along the way. I'm very good at asking questions.
Every facet of a set up is quite complicated. Even power cord's can be challenging. Name recognition is very important and there are so many names.
The technical aspects of everything involved is clearly overwhelming and requires a lot to barely understand. I've learned enough to know that I really don't understand a lot. At least I'm able to appreciate what I'm listening to which is all that really matters, and know if something sounds good.
Just my thoughts for what they are worth.