Depressing yourself is incredibly easy. If you don't believe me try thinking about Global warming, Poverty, War... you get the idea.

It's getting out of depression that's difficult. Otherwise people would go to the doctor to complain that they're not getting depressed enough, wouldn't they? There is such thing as not being sad enough. It's very rare that someone has unipolar mania, but it's common in bipolar disorder to fluctuate between the two extremes.