A "leap of faith" is a metaphorical leap into something unknown, and the reason you take the leap is that you have faith that the outcome will be positive.
For many investors in shares, buying large amounts of stocks in shaky companies is a leap of faith.
Giving away all your money to your church is a religious leap of faith.
Rejecting medical treatment for cancer believing that God will heal you is a leap of faith.
Naturally, not all leaps of faith pay off.