(18) Is the post strong ?
White will try to isolate the enemy outpost by itself occupy the adjacent field 28. This is an active control mode. The idea behind this action is the removal of the outpost of the own discs. The outpost is standing alone and can then be attacked directly. This idea is also called the attack in the back.
At first glance you think the black attack is reliable like this: three attackers against three defenders. However, the danger from the other side.
Because white has now occupied the adjacent field 28 black outpost is cut off from the other disks. The outpost attack three times over 37-31 white wins this disc. Think about it!