I have a hypothesis as to how the token ーン originated and why it's associated specifically with the character Mejiro McQueen. The results from Google Images seem to show that the character is often referred to in Japanese as "メジロマックEーン"—notice the Latin letter E near the end!

Obviously, using a solitary Latin letter in the middle of a Japanese spelling is extremely unusual, but somebody (likely the creators of the character) decided to do it for artistic purposes. (It's a bit like if Toyota Motor Corporation decided to start writing their name as "Toヨta.")

A typical Japanese human would notice that "メジロマックEーン" is just "メジロマックイーン" with the character "イ" replaced with "E." On the other hand, a hand-written computer algorithm would probably be written under the assumption that Latin letters and katakana never occur together in the same word, and so it would treat "ーン" as if it were a separate word.

I don't see any reason to think it's a horse neighing sound. It's not "McQueeeeeeen" either; the plain old "ee" sound in "McQueen" is considered to be a long vowel already, so it's written as "イー" (or, in this case, "Eー"). "McQuinn" would probably be transcribed without the long vowel mark, as "マックイン," but "McQueen" is "マックイーン."

So, I read textbooks "wrong".

The "standard" way of reading a textbook (a math textbook or something) is, at least I imagine, to read it in order. When you get to exercises, do them until you don't think you'd get any value out of the remaining exercises. If you come across something that you don't want to learn, skip forwards. If you come across something that's difficult to understand because you don't fully understand a previous concept, skip backwards.

I almost never read textbooks this way. I essentially read them in an arbitrary order. I tend to start near the beginning and move forwards. If I encounter something boring, I tend to skip it even if it's something I expect to have to understand eventually. If I encounter something I have difficulty understanding because I don't fully understand a previous concept, I skip backwards in order to review the previous concept. Or I skip forwards in the hopes that the previous concept will somehow become clear later. Or I forget about it and skip to an arbitrary different interesting section. I don't do exercises unless either they seem particularly interesting, or I feel like I have to do them in order to understand the material.

I know that I can sometimes get away with the second method even when other people wouldn't be able to. If I were to read a first-year undergraduate physics textbook, I imagine I could read it in essentially any order without trouble, even though I never took undergraduate physics. But I tend to use this method for all textbooks, including textbooks that are at or above my level (Awodey's Category Theory, Homotopy Type Theory, David Tong's Quantum Field Theory, Figure Drawing for All It's Worth).

Is the second method a perfectly good alternative to the "standard" method? Am I completely shooting myself in the foot by using the second method for difficult textbooks? Is the second method actually better than the "standard" method?

All right. The thing is, I don't see how "flow is antithetical to interleaved practice" leads to "flow is a poor ideal for learning", so for me, the sentence "flow is a poor ideal for learning because flow is antithetical to interleaved practice" doesn't make sense.

Actually, I also don't see how flow is antithetical to interleaved practice. The article you linked to says that the "Mixers" (who used interleaved practice) were more successful than the "Blockers", but it doesn't seem to give much of a reason to think that the Blockers were in a state of flow and the Mixers were not.

Can you explain what the diagram means? I haven't been able to come up with a good guess as to what the arrows mean, or how the principles govern what.

You could say that "A and B happen to be in sync for a while" is possibility 3, where C is the passage of time. (Unless by "happen to be in sync for a while" you mean that they appear to be correlated because of a fluke.)

On an unrelated note it se,ems flow is actually the great state for peak performance, but it turns out to be a poor ideal for learning because it's antithetical to interleaved practice.

Would "because it's insufficiently challenging" be at least as good an explanation?