Ever attempt to open a carton of milk, but end up splitting the lip of the carton? Of course, the frustrating battle ensues as you struggle to migrate that final sliver to the other side. Clearly, our pain was heard! Companies began to sell their milk with convenient plastic twist tops to avoid the... Inconvenience... of splitting the carton open. In the end, the change to the carton may have enhanced the product twofold: the seal of the twist top may increase in-fridge longevity, as well as encourage the use of the cartons over non-compostble plastic jugs.
The milk carton serves as yet another example of great re-design with regard to Usability. In this case, it also presented an opportunity to enhance the product as well.
-RTK