Hi David. You asked, "Doesn't suffering cause death to the old man?" I liked what my side-kick Soul man said, and the Scripture he posted Romans 6:6, is a great statement on the results of Jesus' death on the cross....Romans 6:6 "Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin."
Since you, me, and Soul man (not Reba, because she has always been perfect) have been crucified on the same cross as Jesus, the initial sanctification and destruction of the "old man" had it's beginning. Now look at....
James 1:2 "My brethren, count it all joy when ye fall into divers temptations;
1:3 Knowing this, that the trying of your faith worketh patience.
1:4 But let patience have her perfect work, that ye may be perfect and entire, wanting nothing." (KJV)
James 1:2 "Count it all joy, my brothers, when you meet trials of various kinds,
1:3 for you know that the testing of your faith produces steadfastness.
1:4 And let steadfastness have its full effect, that you may be perfect and complete, lacking in nothing." (ESV)
Please notice, "trials of various kinds" That tells us that there will be trials that go beyond the initial death that the old man suffered on the cross with Jesus....Again, your question, "Doesn't suffering cause death to the old man?" The answer is yes. that's where it death to the old man had it's beginning. BUT, since the old man is still with us says the Apostle Paul in Romans seven, we need continual suffering to gradually defeat or destroy the lusts of that old man.
Does this make sense to you?