Quoting Didier Kryn (kryn@???):

> I'm reluctant to use ext3/ext4 because I don't understand why they
> still have this strange lost+found directory, which signs a kind of
> weakness.

It's just a receiving area for fragments (inodes without corresponding
filenames) that might in the future be recovered by fsck. Saying it
indicates a weakness is about as sensible as saying that the presence of
hospitals indicates epidemics. (FWIW, I've never found anything there
since the arrival of ext3 journaling.)

https://unix.stackexchange.com/questions/18154/what-is-the-purpose-of-the-lostfound-folder-in-linux-and-unix