I think we need to define better what you mean when you say “a set of fundamental principles,” because I’m not sure we’re talking about the same thing. Maybe I’ll explain it differently: even if I accept your assumption that there is a set of fundamental principles (which I still don’t understand exactly what they are and why they’re fixed for me from birth and can’t be examined so that I adopt some and throw out others), and therefore I sin in some particular matter, who says it’s impossible to change the weight of each principle in a given situation? If I take an example—I wanted to eat a doughnut even though I’m on a diet—here the immediate pleasure was what I wanted more than the diet. But maybe that’s only because I didn’t think enough about what a diet means—and if I think about it, suddenly I understand that a diet means the pleasure of every new piece of clothing I wear, every moment I look in the mirror, feeling lighter, and so on—has my set of values changed? I don’t think so (although personally I have no problem saying that it has). So what did change? My level of understanding of what the diet will give me. The same applies to the service of God.

And regarding your distinction—I actually think penitents exist within every one of us, not only returnees to repentance.

I’m really not talking about an innate set. A person adopts such principles, and in effect chooses them. I’ve written more than once about this process, which in my view is founded on contemplation and recognition (intuition), not on thinking.
Your description—that you just didn’t think enough—is my answer to the problem of weakness of will. It’s not that you didn’t think enough, but that you let go of the reins of choice.
I don’t know whether you’re listening to this year’s series or an earlier one, but in this year’s series I explained this. There are also columns on the site that deal with weakness of will.
I also think penitents exist within every one of us, and that is exactly what raises the question of weakness of will. You’re mixing up the difficulty with the answer. The difficulty was that a state of weakness of will cannot exist, but in the answer I explain how and whether it nevertheless can exist.

Rabbi, good evening, and thank you for answering—and answering so quickly.
I think there is a difference between my answer and your answer about letting go of the reins.
According to your view, that I can only let go of the reins but not think about my principles and change them—how exactly do I “choose” to let go of the reins? After all, if everything I do is influenced by my principles and they are not the product of choice, how can I choose anything at all? Seemingly you haven’t solved the problem here, you’ve just shifted the focus, and the problem still stands.
According to my view, the question doesn’t arise at all, because I assume (and I think this is the only option) that you really can change your principles. You adopt some of them automatically as a result of education / environment, but you always have the judgment to think about what you’ve adopted. That is basically exactly like anything else in life about which you change your mind.
The novel point from your lecture is that repentance is not only praying and crying to God, but actually applying rational thought to how I fell, why I am where I am, and what I need to do to change it. To think about the process of sin and understand where my failure lies in the fact that I want to sin.

It’s hard for me to keep the thread in mind with gaps like these. Your question about choosing to choose (to let go of the reins) came up in my columns on weakness of will. See there.