Context is everything.
People usually quote this saying to those who are fixated on attaining something that's unreasonable or unlikely.
The other application is for people who want to "Have (keep) their cake and eat it". ie have it both ways.
So the user is basically telling the other person to get over it and focus on something that is attainable.
Some people use it as a throw away line to describe the futility of something they are doing that is unattainable.
People usually quote this saying to those who are fixated on attaining something that's unreasonable or unlikely.
The other application is for people who want to "Have (keep) their cake and eat it". ie have it both ways.
So the user is basically telling the other person to get over it and focus on something that is attainable.
Some people use it as a throw away line to describe the futility of something they are doing that is unattainable.