Are you referring to the saying you want your cake and to eat it too? It's a common saying that means, well essentially you cannot have your cake and eat it at the same time, so when a person says this about someone they are implying the person wants more then they should, can't have, nor deserves. The person wants two incompatible things and they can't have it both ways. Joey wanted Dawson to be her bestie and pinning after her, and date Pacey at the same time. She couldn't have it both ways and refused to see it that way and in the end, while it wasn't her intention, she hurt both of them because she couldn't make decision and stick with it and suffer what ever consequences that followed. What ever she had was just never enough.