The cheerful mother brings up well balanced children even if she is ignorant... and the opposite is true... She may have a PhD and has a gloomy face, and her kids become messed up psychologically.
When the child sees his father gloomy, he translates that into: I am the reason that my father is tired because the child is inclined to feel guilty!
When the child finds his mother angry, he hates himself because he is unable to hate her as he thinks he is the reason behind her anger