So, if you decided to learn a martial art you would be making a self-improvement and as your level of skill improved you would be improving your ability to defend yourself. Now, before you attack the idea that you "decided" thus having free will, the reason you decided is because of inputs that you did not control. The idea popped into your head because of only god knows what (an unconscious, uncontrollable process). Some days when you go to practice your martial art, you will be locked in, focused, ready to learn. Other days you will be distracted by other things going on in your head. What Sam is arguing for is that you strive for the good days, the "present" (my words) days and notice the factors that distract you on bad days and let them fade away. This mindfulness practice (the agnosticist's equivalent of the religionist's prayer) of meditation, yoga, martial arts, etc will help you to increase the likelihood of having good days and your being will grow/learn/improve over time. And as you continue to practice, your ability to draw your focus to the present will also improve, which, IMO, will make you happier.
So now imagine that in some moment you are physically attacked, your instincts and training will take over and you will be better off for having learned the martial art even though you ultimately didn't decide to do it in the first place, at least not consciously. You won't be consciously fighting off your attacker either though it may feel like it. When he hits you, you may not consciously feel the pain because some unconscious process decided that feeling pain won't be helpful in that moment. If you emerge victorious, you will likely feel pride and appreciation that you trained for that moment. But, you didn't control all of the stars that must have aligned that put you in that moment because obviously you would have consciously decided not to get attacked. Indeed the attacker didn't choose either. When you decided to learn a martial art, you felt like you chose because your subconscious tricked you into thinking that you are making decisions, but indeed the reasons to do it were presented to you as the reason you should make this decision and the reasons not to were diminished or perhaps not presented at all. Even if you mull it over, there is only one choice that you could possibly make, the one that is made for you, by you.
Sidenote: I like Sam's characterization of consciousness as a dream constrained by external inputs.
BTW, this has been one of my favorite debates on here, thanks for that. I believe in these concepts because I feel them and observe them. But it seems I lack the vocabulary to explain them. Also, I am not sure that if I could convince you that you don't have free will if that would be helpful to you or not. What I do know is that you won't convince me that I do, and if you were able to it wouldn't be helpful to me. What has been helpful is attempting to explain these things even though it is a bit frustrating as well.