Faith is a principle of action.
Faith proceeds the miracle.
You aren't even going to get out of bed without faith, why would you you didn't have the confidence within yourself that today will be a different day from the day before.
The reason that prisoners and other make tally marks to count days is to make each day a little different. We are not prisoners, we are free to change our minds and thus our circumstances completely.
Viktor Frankl was a Holocaust survivor, because he realized that in his own mind he was not a prisoner he could be anywhere and with anyone he wanted to be.
If you believe you can do something, you probably can, maybe not right away, some things do take time to learn, like climbing a mountain or running in a marathon or becoming a doctor.
When I started out as an engineer I had a dream of working on big things like the Space Program, and in my first job ended up doing just that. Since then I have hit many of my major Life Goals
It is too easy to let someone else decide your level of self-confidence. We were trained that way in school, if you got good grades you were smart if not then you were dumb, but that never took into account how easy and simple the classes were for some and hard for others. Too often the key to an entire class was some small little topic that I found in a book in a few minutes and the rest of the class was daydream time.
At work it is much the same. The boss tells you if you can feel good about yourself or not. Even if he is not talking to you. What does he know? Not you. Your work is different from your life and don't ever confuse the two.
Too often we tell ourselves, "You can't do that" or "Who are you to try saying that" or simplest of all, "Yeah, but..."
Don't hold yourself back. God believes in you so can you.