Has to be more than one reason, just in case the first one doesn't work out, and usually a link to something I already know, say they've played with someone I like. Or they have pipes and/or boxes. Or I like the name of the band, or it's something totally unfamiliar so I think I'd better go and widen the education a bit. Hell, could be anything really! I have no recollection at all of what made me go and see Andrew Cronshaw doing that Finnish thing but boy am I glad I did.