Mutual harm (penetration) means suffering, being killed and being destroyed.
Opposing each other means resisting each other. It's actually a hedge.
As can be seen from the gossip, Mao is wood in the east and unitary is gold in the west (Mao and unitary collide), or fire in the south and water in the north at noon (meridian collision), all of which are relative positions, so it is also called hedging.