It’s not at all uncommon for an artist who is already part of a successful band to start a side project. This page covered one of those fairly recently. Heck, Duran Duran’s members split up between two successful side projects at the same time in 1985. Now, some of these side projects (though probably not Duran Duran’s two) are easily forgotten. Possibly one of the most successful bands formed as a side project, though, was Mike Rutherford’s side project Mike + The Mechanics.
Mike + The Mechanics was so successful that while the band, and several of its songs, are still remembered, other songs which got a fair amount of airplay originally have fallen by the wayside. One of those was the band’s 1986 top 40 hit “Taken In”.