My guess would be that this rule is to cover the case where players stop when they feel their pattern is stable regardless of the rules saying you should do 6 catches. So if I have a pattern with wrong ends, I'll probably quite carefully make my pattern be stable, then stop. But if I attack and have all right ends and am totally in control, I might instinctively stop because I know I've won the point. Even if the rules say otherwise.
You can either change the players to conform to the rules, or change the rules to conform to the players :P
This seems linked to discussion of qualifying after a trick - my general rule for having landed a trick is for my pattern to be as stable as it was before I did the trick, with a minimum of a qualify if I'm not solid on the pattern. So if I do a 3 club trick, I'm satisfied pretty easily. If I do a 5 club trick, I might carry on for 20 catches, drop, and not feel I got the trick, because I never got the pattern back to the state it was if I hadn't bothered doing a trick.
by Brook Roberts, in response to this post 2015-10-27 15:00:08