The centre is the vital point
A three-empty-point space (straight three or bent three) is UNDECIDED: whoever plays the centre first wins. If the defender plays the centre, the space splits into two eyes — alive. If the attacker plays the centre first, the defender can only make one eye — dead. So the centre point is vital for both: defend it to live, take it to kill. Never leave a three-point shape unattended if you can take the centre.