What does it mean when you say you can't have your cake and eat it too?

'To have your cake and eat it too' is to have a dispute settled in your favour well past what would be fair and reasonable, more than your share The law calls it 'unjust enrichment' and tries to avoid it in all settlements The classic case is the engagement ring after a separation, but before the wedding. Assuming the groom paid for the ring, if the fiance says she wants to keep it 'as a memento', for her to keep it in spite of the breakup would be unjustly enriching her and unjustly depriving the ex-potential groom. If she succeeded in keeping it, that would be a case of her 'having her cake and eating it too'