Gratitude is not only the greatest of virtues, but the parent of all others.
~ Cicero ~
You can't be grateful and sad at the same time.
~ A friend's friend on Facebook :) ~
I think it's probably also true (at least most of the time) that you can't be grateful and angry at the same time, or grateful and scared. Making gratitude a part of your daily life can be absolutely life-changing.
One of my yoga teachers often asks us to take one minute of silent meditation to say thank you for everything that comes to mind. I encourage you to try this practice and see if anything changes for you. You can also try a practice like this when you're feeling sad, angry, insecure, or fearful. Bring your attention to the blessings in your life (I promise you there are many), and you will gain perspective. If it doesn't happen at first, keep trying. It will happen.