No, that's not it. Nothing really bad happens when you make mistakes. You're just told you made an incorrect choice, and then it's marked; you can still come back to that Fragment when the time is right. Also, there is no strict ordering required. (There is a bonus if you pull it off, but it's meant to be an extra challenge that you're not expected to get easily. Plus, you're not even allowed to get the bonus the first time you play; you first have to finish the VN at least once.)

That said, please do try to do reasonably well, as having most of the Fragments marked in the aforementioned way is unhelpful. I suggest keeping track of the requirements for each Fragment (probably, write them all down before you start), and be on the lookout for those things in other Fragments. This is something that I think a lot of people try to do the other way around, i.e. by remembering the entire contents of the Fragments, which is not very effective unless you have an incredible memory.

One more thing you need to be aware of: there is one discrepancy between the Fragment dependencies and the textual descriptions. The "Footsteps in the Fourth Year" description specifies two things it requires, but fragmentdata.txt, the controlling data file, gives it none. It's one of the Fragments you can view first.

Thank you for the explanation. But I don't plan to do the VN twice. Will I still get a satisfying ending if I only play it once? I would hate if the "true" ending was stuck behind a second playthrough.

Not a "true" ending. Just a BONUS. Basically a little what-if, with an attached message from the author. Interesting to see, but the VN is still plenty satisfying without it. If you're curious, you might be able to find a video of it or something.

Okay thank you.