For Billy Corgan, it was the beginning of the end after Mellon Collie and the Infinite Sadness.
He appeared bald on stage for the first time
after this album was released, so he wrote the songs while still having (thin) hair. At least he saw himself with hair in the mirror.
After that, the album Adore was not as good, and he may have had the ideas for the some of the songs on that album when he still wasn't sporting a bald head.
Just look at the album ratings:
http://rateyourmusic.com/artist/the_smashing_pumpkins
As the years passed, he gradually "lost it" (sorry for the pun).
Now his albums are just awful, and on top of it, he's a bitter dickhead in all his recent interviews, talking about how he's the best and people cannot see it, and how other musicians are crap.
Now look at David Bowie's career:
http://rateyourmusic.com/artist/david_bowie
Except for that period in the 80's during which he admitted he just didn't give a f-ck, his career remained quite great all along, until the very end.
And you know what else remained quite great until the very end. This is no coincidence in my opinion.
Compare the decline:
And it seems Corgan didn't let himself go only in the music department. He also stopped giving a f-ck about his weight.
