Paul was afraid as he ministered in the city of Corinth. The reason we can believe this is because Jesus doesn't waste words. He comes to him in Acts 18 with an encouragement that addresses his fear.
One of the great hopes of all our lives as followers of Christ is that we can become MORE. More useful, more loving, more gracious, more like Christ, a better witness, etc. Apollos was such a man. We only have five verses in the whole Bible that describe him (Acts 18:24-28
), but look at the phrases God uses.