They have trouble because it is outside the norm and they don't realize it. Sure, sounds easy enough...shoot 5, reload, shoot 5...but how many times do you have an odd number of hits on a target? I bet there are people who can (and do) shoot 6 on each target faster than they can shoot 5 on each target. We train to put everything in pairs with USPSA paper targets, and so it becomes a habit to put 6 where it calls for 5...I agree 100%. Most shooters practice Bill Drills, Blake Drills and 4 aces. We hardly ever shoot an odd number.