The corner is different
Most four-space shapes are alive, but corners are merciless: eye space runs out faster against two edges, and the famous 'bent four in the corner' (盘角曲四) is even judged dead outright under Japanese rules. The habits to build: keep corner groups well-supplied with liberties, and attack corner eye shapes at their bend. Here the corner group's eye space is a bent three — White to play: strike the vital point at the bend.