On Saturday I was going out for a friends birthday so I had to make the choice between whether I was going to flexi syn or have a day off plan. I had used most of my syns for the week already and knew I wouldn't stick to the amount I would give myself and knew I wouldn't count so I decided a day off plan. The next day I counted the amount of syns I consumed and it was way over what I would have given myself. But I brushed myself down and went straight back on plan. Next time I may opt for flexi syn but I knew deep down that this time I would go over what I allowed myself and therefore going against the whole point of flexi syn. I agree that my binge is completely different to deciding on a flexi syn day but think its about how the truthful you are to yourself. If you are truthful and don't hide behind excuses you will easily draw a line under a binge/flexi syn and move on back on plan.
Hope that makes sense, sorry rather long!