That’s literally the defining feature of asymmetric cryptography. There are many explanations of how it works which you can easily find. One example is the Wikipedia article: https://en.m.wikipedia.org/wiki/Public-key_cryptography
If you educate yourself and are still confused, you should probably just accept the fact that even though you can’t understand the specifics, information encoded with the public key cannot be decoded with the same public key.
That’s literally the defining feature of asymmetric cryptography. There are many explanations of how it works which you can easily find. One example is the Wikipedia article: https://en.m.wikipedia.org/wiki/Public-key_cryptography
If you educate yourself and are still confused, you should probably just accept the fact that even though you can’t understand the specifics, information encoded with the public key cannot be decoded with the same public key.