Random Number Generator.

In this case it simply means that all items in the Binding Coil of Bahamut are randomly dropped from a pre-determined list of possible weapons and armor. Thus one person may have their entire Allagan set after three weeks if they get lucky drops. Others may never get their last few pieces. The problem the TC brings up is that Tanks and Healers usually have to lot against each other which makes it even harder for them.