Gogobera: and look to make a second eye, forcing and . I initially thought black could make ko here, after white captures at a. However, white's move is at b. If black captures, white throws in at . Black captures at b followed by white a, leaving black one eye only.
symplicity: There's not even a ko in the "failure" diagram. This is what the position in the previous diagram actually looks like after black's last move. White just connects at a.