I'm a perfectionist. Sometimes, when I don't reach my goal, I get really depressed. 
Is depression a common symptom of perfectionism?
Yes, it happens often. There's a lot of pressure and when we don't reach our goal, it's disappointing.
Can a person be cured from perfectionism?
Well, it's a form of OCD, so it could be tamed with help from a therapist or medication.
I see. Do a lot of people suffer from this disorder?
It's estimated that 1 in every 40 adult in the US has OCD. That's about 2.3 percent of the population, so yes, I believe there are a lot. 
That's more common than I thought. Are there any famous cases?
I assume there are a lot, since such a large number of the population is affected by perfectionism. 
How long has perfectionism been considered to be a serious mental condition by psychologists?
their goals, and to derive pleasure from doing so. 
Definition.
Perfectionists strain compulsively and unceasingly toward unattainable goals, and measure their self-worth by productivity and accomplishment. Pressuring oneself to achieve unrealistic goals inevitably sets the person up for disappointment. Perfectionists tend to be harsh critics of themselves when they fail to meet their standards.
Definition Normal vs. neurotic.
D. E. Hamachek in 1978 argued for two contrasting types of perfectionism, classifying people as tending towards normal perfectionism or neurotic perfectionism. Normal perfectionists are more inclined
of change and people would have moved on after such a long time. Now that I'm moving through my OAP heavy metal years (laughs), I thought a lot of it would be gone by now. And it's a shame. We don't really get to spend a lot of time on this planet together, so there's no point in wasting it being divided."
Halford knew of his sexuality in his youth, and that the current American administration "doesn't look particularly healthy right now.