"For example, a social network for pet owners. It doesn't sound obviously mistaken." It is not obvious so much that actually there are several social networks

"For example, a social network for pet owners. It doesn't sound obviously mistaken." It is not obvious so much that actually there are several social networks for pet owners with apparently hunderds of thousands (registered) users. There is one even in Hungary where I live (only 10million people live in Hungary), but here are some english sites also: http://webtrends.about.com/od/socialnetworks/tp/pet-social-networks.htm http://webtrends.about.com/od/socialnetworks/tp/pet-social-n... Yes probably this is not a huge market, but some people make some money off of this. So, yes, it is totally not obvious what startup ideas are good or bad.