I realize that everyone has different levels of sebum protection, cell turnover, environmental factors, etc. I'm just wondering if you guys have a relatively concise answer as to the actual mechanisms that affect how well a product works on an individual's skin. Why are there so many "hate it or love it" products out there? Is it just psychological? And, knowing more about the reasons why products do or don't work for us, how do we apply that information toward finding more effective products? Thanks!