A word to describe a person whose wishes or desires never comes true

If his dreams are not fulfilled,

John is unfulfilled

From Dictionary. com:

not yet achieved:
his unfulfilled dreams..

not happy or satisfied, from not having achieved one’s desires or full potential:
I was feeling unfulfilled in my job

It doesn't have to be a sad-sack naturally unlucky person. In fact, it could be quite the opposite.

The person could simply have the kind of personality that sets themselves up for failure.

A Pollyanna, an optimist, an idealist, etc. are some types of this personality.

They keep their eye on the goal too much, assuming they will succeed and meanwhile ignoring the possibility that even one of the required intermediate steps will go wrong.