Take the vital point on offence
The same straight three, but now you hold the attacking turn — and on an undecided shape the vital point pays whoever takes it first. Your stone belongs inside the space: played there it splits the eye space in two and keeps liberties of its own, so every White capture spends the whole space and the group still ends with a single eye. The attacker's typical error is filling an end point: White takes the real point, makes two eyes, and your invading stone dies for nothing. White to play: kill Black — take the vital point.