[Jtsummers]

You can treat it like a reverse big-O notation. Your figure out the bus factor for each sub-task/system in your project (this is the risk factor) and then determine the priority of each sub-task/system. If a GUI is "easy" or low priority for your project, one GUI person doesn't mean your project has a bus factor of 1. But if networking is critical and you have one person that understands the novel telecon protocol stack you're using, that's a bus factor of 1.