If you have turned off password protected sharing on a Windows 10 shared folder, you may still notice you can’t connect from a Linux client.
Trying to connect using “anonymous” or “Guest” as the user name does not work – instead try using a space (” “) as the user name and a space for the password.

In fact smbclient seems to work with any username including a space, and the password can be anything except blank.

(Tested with Debian Stretch, smbclient version 4.5.8-Debian)