I think people should try improving themselves by balancing all these characteristics. To be only melancholic, only extrovert or only domineering don't work, we need different elements to fulfill ourselves: it's important to express all the kinds of moods on the right moments (being them positive or not), especially because it can help us preventing diseases and also keeping our mind healthy.
What do you mean by that part I marked in red? Would you mind explaining because it's confusing.
There are people who live only on extremes: totally extrovert or totally introvert, calm or angry, happy or sad... I mean this lack of moods balance in life isn't healthy and can cause diseases.
Think about someone who is constantly pretending to be happy: in fact it's impossible, this person is hiding his feelings. You can find this situation on the work environment easily: there are many people who agree with everything others say or that will follow others orders without expressing they aren't in agreement with that or they will even laugh about a joke that they didn't like.
They are forcing a mood, they are going against their own instincts, what is very harmful on long run. The consequences can be stress, depression, apathy or even an outbreak. That is why I say it's important to balance different emotions and feelings, without hiding anything!