When a child’s basic needs are met, he feels satisfied, connected, secure, confident. The behavior looks “good.”
If a child’s needs are not met, he may feel insecure, afraid, angry, or detached. The behavior that shows, then, looks to be what we might call “unacceptable” as the child reaches out to try to satisfy these unmet needs. This occurs subconsciously, of course; a child is not able to articulate: “You know mom and dad, I have not felt included in the family since the new baby arrived, nor have I felt respected when I speak, so I’m going to be whiny and belligerent for a while.” His needs are valid; his feelings are valid. But he is misguided in his attempts to rectify them.
What we must do as parents is, in the face of misbehavior, remember that 90% of what is going on is below the surface. We must look deep to ensure the child is getting everything he needs, for behavior builds from there.