Note 8 at Acts 18:9: Was Paul afraid? According to Paul's own words, when he recounted his ministry in Corinth he said (1 Cor. 2:3), "I was with you in weakness and in fear, and in much trembling." Paul was afraid and might possibly have left Corinth if the Lord hadn't of intervened.

It is not sin to experience emotions contrary to faith. It becomes sin if we embrace them and allow them to deter us from God's will. We can see by the length of time that Paul stayed in Corinth (v. 11), that once he had God's word on what to do, he overcame his fears.