I once heard someone saying that if Christians behaved like Christians, they wouldn’t have a difficult time believing in Christ, the problem to them was Christians are terrible people.
Christians are terrible people because they are people. We all fall short of the glory that has been prepared for us. We fail to live in perfect communion with the Spirit and therefore we are not perfect.
The difference between a non-believer and a Christian is not the lack of sin in the life of the Christian, but the war that takes place because of that sin and the forgiveness that is received instead of condemnation.