I have in the past built websites where I assumed that Part A would be the most popular part and so put a lot of effort and work into Part A. Less effort was pu

I have in the past built websites where I assumed that Part A would be the most popular part and so put a lot of effort and work into Part A. Less effort was put into Parts B, C, D etc. When I launched it and let it run for a while, it turned out - thanks to analytics - that Part B was the run-away success that was getting lots of search-engine traffic and 90% of the visits to the site. Had I not had analytics then I'd not have known that and would not know which parts of the site people valued. As a result I put the larger part of my focus into Part B instead.