We're afraid when we don't know what to expect, or we expect the worst based on what we conjure up in the imaginings of our minds. When we're grounded in God's word and don't deviate from what that word says, then we have courage.
God gives us His word so we can have the courage to do all He has called us to do. And when we are walking with Him according to that word, we will not only be prosperous and have success, we will have peace and joy.
The enemy only has the power that we give to him. We give it when we are focused on fear-based thoughts. When we are focused on, and believing, the word of God then we are focused on faith-based thoughts. That's when we have the power of Christ in us. That's when we're unstoppable.
Joshua 1:7-9 Only be thou strong and very courageous, that thou mayest observe to do according to all the law, which Moses my servant commanded thee: turn not from it to the right hand or to the left, that thou mayest prosper whithersoever thou goest. 8 This book of the law shall not depart out of thy mouth; but thou shalt meditate therein day and night, that thou mayest observe to do according to all that is written therein: for then thou shalt make thy way prosperous, and then thou shalt have good success. 9 Have I not commanded thee? Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee withersoever thou goest.