Another possibility is that actually it's best to be exposed informally to ideas before you have all the background to understand them completely

IMO, having a road map ahead, even if it is blurry, helps to organize the immediate details. The map ahead will be blurry of necessity, as you don't understand the details yet.

What probably would help for motivation is to see what people can do with the knowledge you're trying to master - see what problems the knowledge will allow you to solve.