You know that feeling of an endless pit in your stomach filled with sludge? It's heavy and deep and you can't lighten it or clear it no matter what you try? You know rationally that there's no reason for you to feel bad, but emotionally you can't shift it. Yeh, me neither.
My mother taught me that I had control over my emotions. It was as simple as choosing to be happy. "Turn that frown upside down." "Pull yourself up by your boot straps." "Wallowing in misery is self indulgent." This way of thinking came with many messages: You're weak if you're upset. You are only worthy of attention when you're happy and accomplished. When you feel bad, you should shove it aside quickly.
So I learned that if I couldn't snap myself out of a bad mood, that there was something wrong with me, that I was deficient, weak. I was ashamed about my lack of control. I carried this through my adulthood, believing that we could be happy most of the time. We just had to try harder to control our focus.