For God has not given us a spirit of fear, but [He has given us by his spirit] power and love and a sound mind. These three things counteract the spirit of fear. We have all the resources of the armor of God, including the shield of faith, whereby we can quench all the fiery arrows of the Evil one (Ephesians 6:10-18). And we have the love of God which casts out fear when we embrace and are completed or matured in that love (1 John 4:16-18).
The last part about the sound mind is not self-discipline. The Greek word is from a verb sophronizo and is a compound word: sozo meaning to save, deliver, rescue + phroneo meaning to think or thinking. Putting those together mean "thoughts of deliverance." These are God's thoughts, His solution to whatever is causing the fear. In Aramaic, the word means "instruction" and is used in 2 Timothy 3:16.
Rick Renner in his book Sparkling Gems from the Greek discusses John 16:13 where the Spirit will "guide you into all truth." This is a quote from his article:
"The word “guide” is the Greek word odegeo and is the word for a guide who shows a traveler the safest course through an unknown country. This means the Holy Spirit is our Guide. He knows the way we should go. He understands how to avoid every trap and obstacle along the way. When we are going into an area we’ve never been before, the Holy Spirit wants to show us how to take the safest route. He knows exactly how to get us safely to our future point of destination."
God's solution casts out any fear when we stand firm and don't go on the path of doubt, worry and fear!