Sayings

Anyone else get fixated on the meanings of sayings? I think I know what all the most common ones mean now but new ones really confuse me. 

I will use some of the most common ones if they make logical sense to me. Like I can understand a saying like that's the pot calling the kettle black because, although it's a bit outdated now, I know that once pots were black and kettles were not. 

But some even when I know what they mean I either think they're stupid or get sucked into well how and why. So I understand the saying you can't have you're cake and eat it too but this one seems a bit stupid to me because I can quite easily eat some of my cake and keep the rest and I then indeed have eaten my cake and still have it. But sayings like the bees knees. Ok I know what it means but why? How does that make sense. Why is something really good being compared to a tiny little knee? What is so great about an insects knees? How does that remotely make sense? And how does something that makes so little sense catch on as a saying that many people use (or at least used to).