In addition to Paul's experience when he encountered Jesus on the Damascus road, he learned from Jesus in the Arabian Desert, and was taken into heaven and given revelations too deep for words. Paul was also given a thorn in his flesh, a messenger from Satan. No one knows exactly what this thorn was, but it is clear God used it to keep Paul humble and to use Pauls weakness to show His strength. God likes to demonstrate His adequacy through our inadequacy.
Scripture References: 2 Corinthians 12:7-10