Why didn't I think of that?

This is sarcasm. The joke is funny because it highlights how unhelpful it is to tell someone with depression to simply 'cheer up.' It's an oversimplification that ignores the real challenges of mental health.

• Depression
• Cheer
• God
• Mental Health
• Happiness
• Therapy

• When you realize you have depression, and depression realizes how stupid you were.
• I don't struggle with depression- like, at this point, I have it down. I'm good at depression.
• Why did you go depressed? Because you’re you.
• When you think you're depressed, but you know you're probably just using depression to be lazy and self-loathing, but then you realize that it, in itself, might actually be a symptom of depression. Well gang, it looks like we've got another mystery on our hands!