pie in the sky

pie in the sky

phase. something that seems good but is not likely to be achieved; unrealistic 

"Hillary Clinton casts Bernie Sanders as an overly-idealistic, pie-in-the-sky lawmaker who won't be able to achieve many of the things he is proposing."

"Those plans to set up his own business are just pie in the sky."

"Those are not pie-in-the-sky and dreaming of those numbers, those are really attainable benchmarks."