I'm willing to speculate in psychology because it is largely a field with few interesting hypothesis and one hell-of-a-lot of Puritan theories.
My thesis concerns tantrums and deep depression, both. I suggest that parents build a switch (metaphorical switch) into the brain of their child for future use in both these circumstances.
I've seen this happen
several times. A child is having a tantrum in public or at home or
somewhere that the child is able to talk to the parent on the phone.
The parent can say something that calms the child. The same seems to
be true for deep depression. I've seen it happen in full grown people
who are in a suicidal depression but when they spend time with a parent
or talk to a parent on the phone they are able to pull out of the
depression.
I see no pattern in the specific nature of the switches. Sometimes the parent is stern (Stop that!) sometimes the parent is encouraging ('You are too wonderful to be doing that') or the parent is merely physically loving and touching.
But I suggest that the switch is important in most people and we would do well to figure out what it is in each case where we have a problem.