This statement can really help to shift our nervous system state when we’re struggling with children’s behaviour. I think there are few, if any, exceptions where children are concerned.
As parents we sometimes see extreme behaviours (and sometimes some very subtle disturbing behaviours) that look and feel deliberate, hostile, mean, cruel.
At the root there’s always something that makes it all make sense. Faulty beliefs about self and others often play a part. If children believe that they are bad at their core then doing bad things is logical and more comfortable at the nervous system level. If they believe they are powerless then they’ll take hold of any power they can and try to present as more powerful than they feel. If children believe their caregivers have hostile motives towards them then they’ll try to defend themselves. It’ll also be easier to hurt adults if they believe adults want to hurt them.
Environmental triggers related to past trauma often also play a part but even without that there’s enough going on internally to keep stuck patterns of behaviour going.
This is why empathy and compassion is so important as we also set clear limits and hold our own boundaries - addressing the behaviour while also communicating/building safety and containment, and chipping away at the core beliefs.