Extremes are risky, so we are most content with the "in between" scenarios. Makes sense.
Another reason why mediums are blessed: as this world is evolving into the era of hybridism, ability to adapt to broad field of ideas works favorably amongst civilized species, and those who can embrace both get to be the ones who flourish. It's the infamous survival-of-the-fittest-schema. Consequently, we see the never-drying well of neologisms, of new terms representing combination of two discreet concepts.
As a Konglish speaker and a biopsychologist, I may be able to say that I am an avid practitioner of medium-ism. I find myself always putting one foot on one side and one foot on the other. I am the happy medium, the middle person, the either/or [or maybe neither/nor]. It's a huge advantage that I have--being able to taste the best of both worlds--but many underestimate that I pay the price of recurrent identity crisis.
Mediums aren't always happy.
Some worlds have things only in black and white and there comes a time when mediums have to take a side.
There comes a time when a Konglish speaker has to decide where she fits more, of whom she wants to work for, and how often she can go without seeing her family.
There comes a time when when a biopsychologist has to discern whether the purpose of her life is to treat patients, to research, or to educate younger generation. Or on a count that she has a womanly goal, she might consider being a homely mother someday too.
Because, all their lives, the mediums have been given with the option of switching to a different side in case where the first option fails, they are not good with choosing just one side. When the reality demands that you just choose one, an unhappy medium just wants to.....fly away.
Like them in Lovers Over the City by Marc Chagall.