People vary quite a bit, so this may only apply to a subset of readers. It definitely applies to me. I learn by working backwards much better than by finding a path from basics to an end result.

Also, for a whole lot of topics, "learn X" or even "study X" is not a well-formed intent. There are often an incredibly wide range of activities you could undertake that seem to be leading to your goal(s), but are actually part of a completely different result that happens to share the same name "know X".

Don't attempt to study machine learning. Pick an outcome you want (perhaps building a LessWrong comment classifier), and study enough to get that done. Then pick another outcome, and do that.

Don't attempt to study quantum mechanics. Instead, try to figure out why you should care about the many-worlds interpretation.