Some products are just a breeze to use right off the bat. They make as few assumptions about the prior experience of the user as possible. eg: iPad, toaster, dishwasher. Using them is a smooth time. (Note that commodities are, by definition, smooth)
Other products have a steeper learning curve, mainly because of many underlying features. Eg: spreadsheets, power drill, emacs. The start is rough, but once the hump is crossed, the utility of the product shines.
Some products are robust - they stand up to all sorts of operating conditions. eg: Toyota Camry
Some products are tough - they perform stellar under certain conditions. eg: Ferrari
Hypothesis: The most successful products (defined by the creator) are either smooth+tough (iPad), or rough+robust (emacs). The best ones, in terms of utility and value creation, are invariably (rough/smooth)+robust
Proof: Left to the reader...