There are few phrases I cannot understand, but there are a lot of phrases I hate:
1) "Science doesn't know everything": Well duh. If it did, it would stop now wouldn't it? Saying that Science cannot (yet) explain X is not an argument that it never will be able to, or that whatever hokey-pokey baloney substitute can explain it. Science once couldn't explain what lightning was. Now it can. Science once couldn't explain how the sun worked. Now it can. Science once couldn't explain what light was. Now it can! You see the pattern?
2) "My Country Right or Wrong". Why would you support your country if it did something wrong? Morality should ALWAYS come before patriotism, in every case, in every instance. If your country does something wrong, a TRUE patriot would point it out and try to correct it.
3) "There are no atheists in Foxholes" - a blatant lie. There are quite a few. Look up the stats yourself if you don't believe me.
4) "It's always darkest before dawn". This makes no sense at all - it's equally dark before 1 hour before dawn as it is 4 hours before dawn (at least in most parts of the world). In fact, juuuuuuust before dawn, the sky starts to get a little brighter. Whoever came up with this phrase obviously never saw a sunrise.
5) "It takes one to know one" - No. It does not.
As for the whole "Have your cake and eat it" phrase, I remember hearing that it was actually "Eat your cake and have it too" originally. This was to say: "You can't eat your cake and still have a cake" - once it's eaten, it's gone. It's been corrupted into the "Have your cake and eat it too" phrase we all hate.