I believe STAND PLACEMENT is 85% of the Battle to kill good deer.
I will give scent 10%, and camo and all the other junk you can think of the other 5%.
I tend to like this way of thinking as it would tend to explain why my success varies so greatly during any given season. However, Bowfanatic also made a very good point. Perfect stand placement is not always possible for a variety of reasons such as hunting pressure, location, limited time, etc...