Well, it depends. Sometimes, one of them is recruiting for a mission and what they're offering is pretty worth it, and they seem able to provide what they offer as well. Sometimes, it can just sounds particularly interesting and manages to appeal to all the characters, either because the person giving the task knows them well enough to manipulate them so or by pure luck.

And sometimes it's just a bit of 'well this sounded like a good idea when I was tipsy/drunk but now we're miles away from town and if I turn back now I'll look stupid'.