The nice thing about this approach is admitting that it's _okay_ if you skip an exercise you're struggling with. It can be a little frustrating at times, and feed a little bit into that insecurity, but a key realization is that one programmer can't possibly know everything. Not in this field, it's way too big. So, skip it! If it bugs you, come back to it in a month or so and you'll be surprised at how much easier it is on a second pass. Or, you'll have such a strong grasp of the language that you'll see, "Ah, there's the fundamental element I don't understand, here's what I can search for, or who I can ask to point me in the right direction."
I agree, but only if you tried really hard. I believe that the main benefit of exercises is not so much getting the right answer (who cares anyway?), but the fact that they made you go over and over again over the concepts, forcing you to really understand, to reread your notes, and to apply them, even if you fail at first. If you do this, it will stick, and, as you said, the next time you come across said concept you will be much more likely to get the subtleties and, suddenly, that mother of a problem becomes trivial.
