There are a lot of clichés that may not make a lot of sense at face value. I've found some actually go a lot deeper than you expect, or may actually apply on multiple levels. Common wisdom often hits harder than I initially realized as I've gotten older...
Edit: and as you comment shows, I've also been guilty of straight-up misinterpreting the meanings as well. Literally just the other day i realized that Lifesavers™ candy are supposed to be little life preservers, as one would have on a boat. For whatever reason, i thought they were just making some grandiose claim as brands often like to do... Sometimes our first impressions become our impressions until correction which may not take place for a long time
I've only had this phrase explained to me recently, and since then I can't help but think it would make more sense if it was told the other way around; such as "you can't eat your cake and have it too".
The problem is, that is the cake's sole purpose. If it isn't consumed it doesn't mature and yield more cake. The analogy is a well known idiom, but it sounds a bit short when you think about it.
I think it's more about restraint versus instant gratification. When people have cake it's usually meant to be shared in some kind of party, so if you go ahead and eat the cake alone you miss out on the sharing which could be said to be the cakes original purpose.
It’s a reference to a very pretty cake. Imagine a wedding cake on display at the wedding, before the bride and groom cut into it. They want to keep the cake pristine so it can stay on display. But that means they can’t eat it, because eating it would destroy the art. They also want to eat it, because it’s cake. They want to have their cake (to display) and eat it too.
I don't understand why society demonizes that (the multiple people thing, not the lack of communication). If that's what's best for my partner, who am I to stop them? What does exclusivity even get me besides limiting my jealousy?
If someone needs multiple partners in their life to feel fulfilled, then wonderful, but they just have to make sure that everyone involved is fine with that before they get into the situation.
Polyamory is very cool for people who are wired for it. A whole lot of people aren't, and that's okay. And some people could be wired for it, but they have a whole lot of self-work to do before they'll practice it well.
It works for me because I know that I never again want to presume any semblance of control or authority over any partner's absolute right to seek out joy and fulfillment by forming however many ethical and consensual relationships they wish, of whatever style they wish, with whomever they wish, for as long as they wish, and I insist upon the same right for myself.
Jealousy is just not an emotion I experience. Envy, yes...envy being wanting what someone else has. When I see a partner of mine having a particular dynamic with another partner that I want to have with them, I feel envy. But not jealousy, which is not wanting someone else to have something of yours. That is, I don't feel anxiety about their other partner "stealing them away from me." Anything lacking between me and a partner has nothing to do with anyone else not in our relationship; if I feel something is missing between us or want things to be a certain way, it is incumbent upon me to speak up, and vice versa. Outside of our relationship, I cheer my partners on in their other connections because love is fucking amazing, man!