Re: American Idol's after Idol...
The industry, itself, is highly luck-dependent. In a way, exposure on AI, itself, is just one manifestation of luck, for the contestants but there are no guarantees. Therefore, the main differentiator between contestants who do well after AI and those who don't is often a matter of whether or not they get yet-even-more luck.
For example, Jennifer Hudson was cast in what for her could very well be the role of a lifetime (Effie White). Without it, she may be nowhere, today. By the same token, without AI, it is possible (but far less likely) that Hudson still could have gotten lucky, and gotten that part, and made her career. Or she might have hit it big in a completely different way. Or she could have had some bit of misfortune that derailed everything for her. That's not to say she isn't talented -- she is -- but many people equally talented never make it big, because of luck.
I do suspect that some people simply have so much talent that they'd do well, somehow. Chris Daughtry probably qualifies. He might not have been a lead singer for a top rock band, but his talents are so strong that perhaps even without luck he'd have made it big. However, that's really rare. David Cook, for example, a contestant in the same vein as Chris Daughtry, did better than Chris Daughtry on AI, but his talent probably isn't big enough to overcome a lack of luck, should that come to pass for him.
Just a clarification: Chris Daughtry didn't get hooked up with better songwriters. He is that better songwriter that perhaps could have made the difference for some of the other contestants. He wrote or co-wrote ten of the cuts off his first album, including three songs he wrote solo, including one of the biggest hits, "Home", which peaked at #5 on the Hot 100 and at #1 on the UK singles chart.
Contrast that with Taylor Hicks, who got "hooked up" with songwriters such as Rob Thomas ("Smooth", "Lonely No More"), Corey Rooney ("I'm Real", "If You Had My Love"), Kara DioGuardi ("Sober", "Bella Tracion"), etc. That didn't seem to make a difference.