Potty Training!

So 'M' potty training is like this. She can stay dry and even tell me on Fridays. Only on Fridays. Hmm. Wonder why? So today I asked her, "Why do you stay dry on fridays but not on the other days?" 
'M' response: "Too bad for you." 
(other 3 kids were trained in 4 weeks, guess I needed one difficult one)