What's interesting is that neither team consciously decided not to collaborate. Instead they did what came naturally, which is to work either completely or partially on their own. The reality is that true collaboration is difficult. It requires subordinating individual goals to collective achievement; it means engaging in tough, emotional give-and-take discussions with colleagues about strategies and ideas; and it often leads to working in new ways that may not be comfortable or easy. So given these difficulties, most teams find it easier to talk about collaboration rather than do it.
