Dictionary definition: “requiring more than usually expected or thought due; especially great patience and effort and skill”
Imagine having a broken leg, you know there is treatment and with a little patience you will be better before you know it. With a personality disorder you are likely to experience the problem for many years with no real hope of a cure but your symptoms are likely to lessen as you grow older. Unlike a broken leg, you can not exactly see what is wrong but you can definitely feel it. I am sure everyone will agree this would make anyone quite demanding and impatient.