I wondered about this for years and years, never understanding, especially, since "having cake" and "eating cake" are used interchangeably. But, I finally figured it out! In this sense, the "having" is equivalent to "keeping" or "being in possession of."
Examples:
- "What's it like having a Mercedes Benz?"
- "The Smiths have a very nice home."
No eating implied!
Therefore, the saying is more inline with "You can't keep (to show off or admire) your cake, and eat it, too."
My least favorite is
Even in grade school I knew this was hogwash. I didn't act the same in class as during recess, or in church as when at the dinner table. Exactly which me was I supposed to be? When someone asks, "What am I supposed to do?" They are really asking, "How should I behave?" And if you've never been on a date before, or this is your first job interview, then it's not obvious.
A: "So, how did the interview go?"
B: "Not so well, he threw my resume away, in front of me, and ordered me to leave."
A: "What? Why?"
B: "Well, I did just as your said, I was being myself. I walked in, gave him the ol' finger guns, then started with my best fart joke."
A: "Why the hell would you do that at an interview?"
B: "Because that routine always slays in the dorms and I was trying to be myself."