Sorry if I'm really stupid but I don't get this
You can't buy anything new until you've finished all 10 stuff? So I can't get a new cleanser until my moisturizer is finished, etc.. or is it I can't get a new cleanser until my current one is empty?
Well, usually according to the "rules" you can't buy new products until you have finished all 10 products. But I guess the key thing is that usually people who would commence a P10P have LOTS of stuff to use up. They don't just have one cleanser, one moisturizer etc. but to something extent excessive amounts of everything.