Emotions have evolved as the mind's way of shooting from the hip when gauging priorities, in order to protect our own interests. Something that triggers little or no emotion is typically an unimportant event which requires little attention, while something that causes high emotions is just the opposite. Fear, anger, happiness, confusion... these and other emotions all originate as signals from the subconscious to separate the trivial from the important, and they make highly useful logical shortcuts in decision-making. When stripped of this ability, the mind loses much of its effectiveness in prioritizing, causing the relevant and irrelevant to be given incorrect relative importance. For this reason, persons with alexithymia tend to be highly indecisive and inconsiderate.
As a side effect of their condition, alexithymics have impaired senses of imagination and creativity. The mind usually combines emotional information with rational when imagining scenarios, but the alexithymics' will be missing any emotional content.
Some cases of alexithymia are neurological, meaning that it is caused by a deficiency in the brain pathways that process emotion. Others develop psychological alexithymia as a self-defense measure against the emotionally indigestible, such as terminal illness, or post-traumatic stress disorder. As a coping mechanism, the mind simply shuts down the pathways that process emotions, resulting in a stoic, emotionless state. This type of alexithymia is usually reversible through psychotherapeutic means, and sometimes with the help of anti-depressants.