English to German Art/Literary Idioms / Maxims / Sayings Tao Te Puh

Hello, this is a sentence Winnie, the Pooh says in his book: Tao Te Puh (DE) or Tao of Pooh (Eng).
I did not read the book in German, somebody did and remembers how this was translated? I only could google that the translation differs quite a bit.

I would think of something like:
Eine Fliege kann kein Vogel sein, aber ein Vogel kann fliegen.
or
But if I do it completely free as "Eine Fliege ist eine Fliege und ein Vogel ein Vogel

But nothing convinces me really.


Regarding the meaning I found here:
http://www.thecottlestonpie.com/whythecottlestonpie

“A fly can’t bird but a bird can fly.” Very simple. It’s obvious, isn’t it? And yet, you’d be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are. It is useless to try to make things into ways they’re not. Everything has its own place and function, including people, even if they don’t realize it, and that’s why they keep the wrong job or stay in the wrong marriage or relationships. You need to learn to know and respect your Inner Nature. When you do so, you know where you belong and where you don’t belong. “A fish can’t whistle and neither can I”. This means “I have certain limitations, and I know what they are”. There’s nothing wrong with not being able to whistle, especially if you’re a fish. But there can be lots of things wrong with blindly trying to do what you aren’t designed for. That doesn’t mean that we need to stop changing and improving. It just means that we need to recognize what’s there.

Thank you!