What is Espresso coffee is a very bitter?

I often hear many people Ironically, the self-stated as "espresso fans" heard espresso coffee as a super bitter. According to my opinion is wrong.
Indeed bitter taste in the coffee because naturally caffeine content, but should not become the dominant taste. Excessive bitter taste and lack of flavor usually caused by an error extraction. Extraction temperature is too hot for example, can burn the bitter taste of coffee so that more prominent. Robusta coffee also feels more bitter because the caffeine content is much higher than the Arabica Coffee. Espresso is extracted correctly has a sweet taste and a natural component of bitter and sour taste that balanced.
Brown also have a bitter taste is not natural? But I am sure you will not become fans if chocolate taste bitter taste more dominant than the other.