Acts 18: Paul was afraid in Corinth.

 Corinth was worse than Las Vegas:
AI: Corinth was the "Sin City" of the ancient world. It was a place of extreme wealth, intense idol worship (the Temple of Aphrodite had 1,000 ritual prostitutes), and litigious, aggressive people. It was an intimidating environment for a small group of tent makers.
Paul came from Athens, where he was mocked by the intellectual elite.
Paul had been already experienced persecution in many cities.

9 And the Lord said to Paul by a vision at night, “Do not be afraid any longer, but go on speaking and do not be silent; 10 for I am with you, and no one will attack you to harm you, for I have many people in this city.” 11 And he settled there for a year and six months, teaching the word of God among them.

Imagine the joy to listen from Jesus: "I am with you". Besides, Jesus told him there were many Christians in Corinth. Paul was certainly not alone.
Jesus kept Paul on the way, strengthening him.