Word for person always after what he does not have and not cherishing what he has [duplicate]

Possible Duplicate:
Term for “constantly unsatisfied soul”

Is there a word for a person who is always after what he does not have and does not cherish what he has? If not, any idiom or phrase?

No single word comes to mind (though I wouldn't be surprised if such a word does exist) but a certain well known proverb does:

The grass is always greener on the other side.

The Free Dictionary defines this as People always think they would be happier in a different set of circumstances. (Usually implies that the other circumstances really are not any better.)

Sounds like an ingrate to me.

If to be grateful is exhibit these qualities:

appreciative of benefits received : willing or anxious to acknowledge and repay or give thanks for benefits

Then an ingrate exhibits exactly the opposite.

A malcontent is such a person. Relevant excerpt from The Free Dictionary (formerly The Free Online Dictionary):

mal·con·tent (măl′kən-tĕnt′). [...] n. 1. A chronically dissatisfied person.