That all sounds right to me.
Yes, if you’re considering asking for a phone number based on what seem like unreliable clues, you’ve likely noticed that you’re considering asking for a phone number based on what seem like unreliable clues. That’s something where you’re quite likely to be wrong in a way that stings, so you’re likely to notice what you’re doing and rethink things.
When the cashier smiles at you 1% more than usual, you probably don’t stop and wonder whether it’s a sign or not. You won’t think anything of it because it’s well within the noise—but you might smile 1% more in return without noticing that you do. She might smile an additional 1% the next time, and you might respond in kind. Before you know it people might be saying “Get a room, you two!”.
Even if she then asks you out—or you ask her out—it was the subtle iterated things that built the mutual attraction and recognition of attraction that enabled the question to be asked and received well. In that same situation, if you would have responded to that first 1% extra smile with “WILL YOU DATE ME”, she probably would have said no because she probably didn’t actually like you yet.
If you do ask her out, and she says “Yes”, do you credit the fact that you explicitly asked, or the fact that she smiled that little bit more? Or the fact that you smiled back that little bit more and played into the game?
Yes, there are obviously many instances where men feel like their only chance is a leap of faith, and men tend to notice when they’re contemplating it. In absence of opportunity to iterate, they might even be right.
At the same time, much of the work—especially when done well—is in responding to things too subtle to be overthinking like that, and iterating until the leap takes much less faith. I’m not taking any hard stance of when you should take a leap of faith or not, but I am pointing out that with enough iteration, the gap can be closed to the point where no one ever has to ask anyone anything.
Notice the presupposition that “tensing your muscles” is the default way most that most people hold their arm straight? Notice how in the video you linked he explicitly specified “really tight” and didn’t just say “don’t let me bend your arm”, letting people do what actually comes by default? They seem to always specify to make the arm tense, which is unsurprising because if you’re not told to resist wrong, you might not resist wrong and then their trick won’t work.
I tried it with my wife, only instead of saying “Hold your arm really tight” I just said “Don’t let me bend your arm”. As a result, she didn’t foolishly contract her bicep to help me, and was able to resist just as well as when I told her to visualize stuff. It’s not that visualizing firehoses is unusually effective, it’s that you’re getting bamboozled into doing it unusually ineffectively to start with.