When you done your part. A crew is a bit like an arch support. Sure, there's a lot of hype about the keystone being everything to the support, and sure, that's me, Mr. Keystone, though you can call me Foreman or Boss. But less well touted is the fact that every part of the arch is its own keystone! It can take an incredible load, and stand alone without extraneous support materials saving costs and keeping up with classical design ideas, but most of all, it will fall without ANY of the correct pieces! THAT'S what a crew is, and you're part of it! Or doing your part in it. Followin' me here? Arch supports are good for doorways and bridges! Well. And cathedrals if you're into that.