Why "ls" doesn't show the file that "find" discovered?

In Unix, a filename beginning with a dot, like .erlang.cookie, is considered a hidden file and is not shown by bare ls. Type ls -a to also show hidden files.

From man ls:

   -a, --all
          do not ignore entries starting with .

However, you can show a hidden file with ls if you specify the name:

$ ls .erlang.cookie

In Unix, hidden files start with dot(.), so when you issue "ls" command it will not list them out. If you want to print hidden file with long listing format you can use following command,

$ls -la

l - use a long listing format
a- do not ignore entries starting with .