"I initially had the same experience as most of the other commenters who said that the shoe causes blisters in the upper part of the back heel. My skin is particularly sensitive, so it sure hurt. But then I started wearing liner socks to avoid the blistering, and the situation improved immensely within just a few days. I guess it really widened the back-heel area to the point where I don't have to wear the socks anymore (though I still do on occasion). There's also more give a little more to the front and inside of the foot (I can see the shoe widen a bit as I walk), which I think is why it feels better. For a shoe that I, like others, felt I needed as a staple for my wardrobe, the break-in period was well worth it. :)"