Now I understand. This may confuse for sure even experienced user. Because if there are many wallets around, it may happen that the user completely forgets about existing passphrase.  

notgeld

bitcoin

Why seed phrases are bad?

If I I put a seed phrase and supply a pass phrase, my client will generate a private key. But, the client won’t store my passphrase. 

So later, if I export my private key as a seed phrase, it will be different from the one I first supplied.

This will confuse some people, for sure.