yes they are not that comfortable... they can cause pain if worn for too long or on longer distances...
http://en.wikipedia.org/wiki/Flip-flops
http://www.huffingtonpost.com/2013/0...n_3569222.html
http://www.huffingtonpost.com/john-w..._b_844981.html
try buying some other ones like Raider or Nike and if those are not confy stop using them...