Something unattainable is out of reach — you can't attain it or achieve it.
Unfortunately, a lot of things in life are unattainable. For most of us, making a billion dollars is unattainable. Marrying a famous movie star is probably also unattainable. Flying to the moon in a private space yacht is totally unattainable. If something is unattainable, then you just can't get it. In life, it's not always easy to see what's unattainable and what's attainable, which can cause a lot of frustration.
