You experience God's power and presence in your life every day. They speak highly of Jesus. They may even pattern part of their lives after Jesus, but deep down they are not really sure that Jesus is real. They have not experienced the presence and power of God in their lives. If you are going to tell others about Christ effectively, then you must talk about Him from your own personal experience.
Personal experience makes all the difference.
For example, the way you tell someone about the new roller coaster you heard advertised on TV at Six Flags is one thing. You need to know without a doubt that you are experiencing God's presence in your life daily. Recall two times that you felt close to God. Possibly you have felt so close to God that it was as if He was with you physically. Or maybe you have never felt particularly close to God.