Memorization. And it's not just any memorization, it's memorization on a level I do not comprehend. Basic patterns like symmetrical sliders, diamond jumps, or linear/simply curved notes I can get, but on complex songs with weird jumps and spacing, I don't understand how people do it. For 700+ notes. In <30 tries. I mean, I know there's a lot of potential for cheating, but I know a lot of people do it legit, and it blows my mind. Especially HD+FL, where you're just flying around the screen trusting that there's a note where your cursor lands. When I try FL, I usually remember generally how a pattern will go, but I don't remember exactly where the notes are, so I'm bound to miss one by a few millimeters eventually.
I'll stick to HD and DT. You scary legit FL people can go back to the moon.