<I've never met a programmer (including myself) who knows as much about how my customers use the product as product managers or marketing people do.> In my exp

<I've never met a programmer (including myself) who knows as much about how my customers use the product as product managers or marketing people do.> In my experience, customer/product support people (pre-sale and post-sale) have a better understanding of product usage and needs than programmers or marketing people.