I feel you, the only reason why you are losing them after watching those tutorials is because you have not found the importance of those concepts.
Say if i intend to build an iPhone app, i can go all out reading 3-4 books over and over again? By doing just that, i will definitely lose all those concepts in no time..
Why is that? Because i dont know what this is used for, which is important, and i will assume that once i've read it i totally get it...

What should you do? Build something real! You could pushover converting existing apps to a later date.
Start anew, create a new application from scratch, and start understanding what's going on. Experiment what if i take out this code, what happens? And when you're stuck, start referring to books, google, etc..
Once you've solve it, that's when you get it. Doesn't mean you will totally get it, but at least you know this is what i have to do in order to get that done (added to your toolbox). Then as you keep doing them, you will know them by heart.

Self training is possible. So get out there and build something real, build something simple. You'll be surprised! Good Luck!