When he was known as Saul, Paul was a respected member of society. He was learned. His zeal probably earned him a lot of honor among the religious leaders of his day. He probably had what we would call a good life.
But when the truth of that matter is unveiled by the Lord, whatever worldly acclaim and honors and comforts Saul enjoyed, he was not happy. His life was hard and unsatisfying. To use the Lord's words "It is hard for thee to kick against the pricks". That is a statement of what kind of life Paul was leading. It just all seemed wrong and unsatisfying. It was hard.
Afterwards we read of Paul living a life that involved great suffering. Paul was scourged, which was such a horrific punishment that many people didn't survive scourging. Paul was eventually imprisoned and, we believe, executed.
And there is something interesting in the fact that it was the first half of Paul's life of which the Lord would say "It is hard for thee to kick against the pricks" rather than the last half. The last half involved great persecution and suffering to be sure. But these burdens were swallowed up in Christ. They were light compared to the burden of fighting the truth.