i see where you're going with this... I felt this way too when I first started out... I wanted to master this one concept first before I move forward and add a new concept to the mix. The thing is...as I moved forward, the more I learned, the more it helped me understand stuff I didnt grasp at first. Okay, that whole thing just confused me, let me back up.
As I moved through FCC and saw how these little parts I learned from Kyle worked together as a whole then it ALL started to make sense...and on reflection, the course didnt suck at all...it was actually pretty amazing! Its just that I needed to know not only what the puzzle pieces were, but how they all fit to work together to fully understand what I was looking at.
So yeah...basically, you cant mater one concept before moving onto the next, because they are just smaller parts that work together to make up a whole moving part. The more you learn, the more you'll understand the previous stuff you learned. Its definitely a good idea to look back on prior lessons..you'll find that stuff you didnt quite understand will make a lot more sense.