"If you believe in yourself, you can change the future."

There are so many supposedly motivational quotes out there that urges you to be yourself or believe in yourself, but my question to them is, how? How do I bring myself to really have faith in myself? They say that the key to conquer your struggles is always to have faith in yourself. But then, how? How do you believe in yourself when you lack the confidence to do so? 

I've thought about how believing that God is there to help you through or praying will increase the amount of faith one puts in oneself. But then again, doesn't that mean that you're merely believing in God or some other greater force rather than yourself? Sigh it's not that I have low esteem or whatsoever. I'm just trying to be realistic. It's hard to believe in yourself at things you're obviously inadequate at...