The problem with my friend was that, although he wrote the seed phrase somewhere, because wallet apps like that usually ask you at least some words of the seed phrase before creating the wallet, he didn't think that it was important to save it 
because he thought that the fingerprint was enough. But: what if he'd lost his device? there are so many things bad about what he did, I couldn't believe it when he confessed me his loss.
This means that he was negligent because he did not consider the seed phrase to be important, so this is a bad disaster. because he thought that the fingerprint was enough. But: what if he'd lost his device? there are so many things bad about what he did, I couldn't believe it when he confessed me his loss.I used to experience something similar but the case was a little different because I intended to store a little bitcoin in my mobile wallet but somehow after the update my mobile app suddenly restarted itself which caused it to ask for the password again, while I forgot the password using only my fingerprint.
So I learned from this that saving a seed phrase is important even if it's just for a temporary wallet.