I've been told that asymmetric cryptography requires that the message to be encrypted be smaller than its key length. Why is this?

I know about hybrid encryption, which uses symmetric encryption to resolve this problem. But I still want to know why public-key cryptography needs the data to be shorter than the key length.

I've been told that asymmetric cryptography requires that the message to be encrypted be smaller than its key length. Why is this?

I know about hybrid encryption, which uses symmetric encryption to resolve this problem. But I still want to know why public-key cryptography needs the data to be shorter than the key length.

Asymmetric cryptography can generate huge keys and make it almost impossible for people to crack without a super computer because it will take a very long time to cipher/decipher anything if your key is big .e.g 4096 bit key.
What I know is you can only cipher data that is smaller than the Key length.
  I also know a method called 'Hybrid Encryption' which uses Symmetric encryption to resolve this problem, as explained here:
http://stackoverflow.com/questions/3491481/encrypting-large-files-using-a-public-key
  However, my question is why does it need data smaller than it's Key length?

I've been told that asymmetric cryptography requires that the message to be encrypted be smaller than its key length. Why is this?

I know about hybrid encryption, which uses symmetric encryption to resolve this problem. But I still want to know why public-key cryptography needs the data to be shorter than the key length.