Super question. I always have liked such question.
Believe you can and you're halfway there.
A person looks in the mirror and finds his competition there.A bird sitting on a branch of a tree is never afraid for it to break,as it's trust is on its wings.
For instance, you are given a task to do in limited time frame.Help is provided,task is difficult.You think you cannot complete it.A tiny push from your side to believe in yourself to do in on time can do a lot of miracles.
Life is about ups and downs,lows and highs.Its all in your mind,whether you want to do it or not.
When God pushes you from the edge of a cliff,trust him fully and let go, cause either he will catch you when you fall down or teach you how to fly.
The word - belief is however simple but has a real compact meaning.It you who will have to dig in to find its true meaning