I went to a conference where I needed to look somewhat professional, but I needed to be able to walk several miles and stand for several hours.  So, I went shopping for a pair of black flats.  I tried three brands of shoes that were relatively cheap – $30 to $60.  Even though they all had reviews praising their comfort, I was uncomfortable in all of them.  Then I found these.  More expensive, but worth every penny.  They were so comfortable that I wore them even when I didn’t have to look nice.