Consistency wins the race

Everyone has an area where the energy never runs out, and another where it suddenly disappears. Two upside-down letters Nun frame the pasuk of "Vayehi binsoa haaron" in Behaaloscha, and the Gemara in Shabbos says they separate three episodes where Bnei Yisrael sinned, so it wouldn't look like a pattern. Then why is the break placed after the first one, and not just before the third? And why a Nun, of all letters? In between comes Eliyahu HaNavi meeting a fisherman who says he's simply not smart enough to learn, and the gap in our own energy starts to say something.