Without the temperaments the world would be an exceedingly dull place, not only ethically, but also in a higher sense. The temperaments alone make all multiplicity, beauty and fullness of life possible. Thus in education it would be senseless to want to homogenize or eliminate them, but an effort should be made to direct each into the proper track, for in every temperament there lie two dangers of aberration, one great, one small.
One danger for the young choleric is that he will never learn to control his temper as he develops into maturity. That is the small danger. The greater is that he will become foolishly single-minded. For the sanguine the lesser danger is flightiness; the greater is mania, induced by a constant stream of sensations. The small danger for the phlegmatic is apathy; the greater is stupidity, dullness. For the melancholic, insensitivity to anything other than his own personal pain is the small danger; the greater is insanity.
Source: Rudolf Steiner – GA 57 – The Four Temperaments – Berlin, 4th March 1909