What do the setbacks of our lives mean? I'll tell you what they mean. They mean God loves you enough to forestall your "forward" progress to ensure that you're getting closer to Him.
I can't answer specifically for anyone. I will attempt, however, to qualify setbacks, disappointments and defeats under two categories:
• Watersheds: Also known as turning points, epiphanies, Aha!/eureka moments, etc.
• Waterloos: Crushing defeats (though not really if you're still alive).
As God sees everything we don't, we'd do well to realize that any setback we face is an opportunity to pause and pray. Any endeavor worth its salt is bound to encounter opposition. This is true in the world's system as well as in the church. It's important that we slow down and see that, whatever it is that God is doing or wants to do in our life is undergirded by prayer, praise and worship. This way, any setback you encounter will end up strengthening the project as a whole. And as God is the one "with whom we have to do" (Hebrews 4:13), we know that we're on His time schedule. Areas of blindness in ourselves and others can only be revealed through waiting. Setbacks.
Watersheds come when God says "friend, come up higher" (Luke 14:10). God's call on your life is entering the next phase and yet, there are things that you were blind to. Through it all you remained humble before God and now He's ready to reveal things about your life and call that you weren't aware of before. What's really strange is when God shows you something that was there that you didn't even think to look for. Watersheds. Your life is then qualified, not only by God, but by "before" and "after". Stay humble.
Waterloo: Historically, the sight of Napoleon's ultimate defeat. Prior to that, he had announced in a fit of pride and arrogance that he himself was God. And you know that God wasn't going to allow that. There's only one God. We'd do well to remember this too. Our gifts and callings are "without repentance" (Romans 11:29). This means that our talents and dreams will play out even without God's involvement. Should you run up against defeat in an area of your life where maybe you weren't enthroning Jesus as Lord, then stop and pray. Repent for making a god out of the task or project or even yourself. Humble yourself before Him and ask Him to take over whatever area is in question. God "works all things together for our good if we love Him and are called according to His purpose." (Romans 8:28) Personally, I wouldn't want any endeavor to succeed that was not "according to His purpose".
Setbacks are not meant to make us ultimately give up, just to give up control to God.