A good lesson in the distant opposition. I always visualized it as the opposition plus a knight move.
This position is covered in Fine’s Basic Chess Endings.
“Black must never remain more than one file to the left of White on his march to the K side. i.e. if the W king is on the e file, the black K must be at least on the d file. Consequently, with the B king on b6, and the W king on c4, black to play loses, since he must play to the b file to prevent Ws Kc4,b5”
There’s an obscure oversight pointed out in Fine’s analysis by Norman Whitaker & Glenn E. Harleb’s in Selected Endings. What Fine overlooks is that after 1. Kb2 Kb7 2. Kc3 Kc7 in his preamble, he has exactly the same position as after 5 moves of the correct solution – but he now moves Kc4? and duly gets nowhere.