Finding My Way : Humans & Satisfaction

Humans will never be satisfied with whatever they have. This is one line that I would strongly agree to. It is bewildering to know that humans, well, homosapiens are usually never really satisfied with whatever they have. They always want more.

Ladies who are thin, crave to be fat by eating their hearts out.... they don't gain an inch on their waistline.
Ladies who are .... chubby on the other hand, happens to try all sorts of smilling remedies, exercises, diets, and even go to the extent of vomitting after meals or not even eating at all just to be as thin as the supermodels they worship on screen.

Another example of humans not being satisfied with themselves or what they have would be...hair. If one has naturally straight hair, they would perm it just so they'd be satisfied with their look.
If one has curly hair, they would spend hundreds just to make their hair as straight as uncooked mee hoon.

This goes out to prove that humans are never satisfied with what they have.

Why do these sort of mentality exist in humans? Do they not appreciate what they already have? Do we have to wait for a disaster to happen to make us realize that we in fact really do appreciate our lives and be satisfied with whatever we already have?