A wise person once told me that everything is temporary. This is especially important to note when you are feeling sad, depressed, or down on yourself. Whether you're feeling blue because you got bullied in school, lost a loved one, got rejected from school, fired from your last job, smashed into a car, dumped by your ex-boyfriend etc. Those horrible and what feels like inescapable feelings of suffering will subside. Eventually.
What you have to remember is that no matter how gross or sickly you are feeling, it will go away and soon you will be laughing again. "Shit happens, and then you move on". However, some people take longer to move on than others. I used to think I moved on very fast but that was because I didn't take the time to grieve on my "misfortunes" and I just jumped the gun to get away from the hurt. I soon learned that I was repressing every little ounce of the pain by attempting to move on too fast. I learned that because once something or someone "triggered" me, I wept like a thousand babies without their mothers. I was drowning in my own self pity.
That is no way to live...do not be a prisoner to your own feelings of self doubt, self pity, and self hatred. Yes, it's true that no one else cares, but because we're our own worst critics, once it rains, it just keeps pouring (this I know is true). But guess what? Even the pouring rain will stop. Once you understand this simple concept of how everything is temporary, you will be more than OK.