One Leg Longer than the Other or Uneven Pelvis

See this guy here, in the video? He's got an uneven pelvic bone. The left side is longer than the right. You can see it when he takes a pedal stroke. On a saddle that is not designed to accommodate this type of anatomy, he will experience considerable pain and saddle sores. 

If you suspect you have one leg that is longer than the other or an uneven pelvic bone, try turning your saddle toward the pain or toward the longer leg.