My mother recently lost her phone and I immediately helped her remotely lock it with Android Device Manager using a 17 character password (yeah, that's an odd length for a password but it ended up that way). To our surprise the phone showed up at home as phones often do but unfortunately the phone could no longer be unlocked. Android Device Manager allowed us to set a 17 character password, but Samsung limited the input of the lock screen password to 16 characters, we had one character too many.
The worst part of it all was that when we tried setting a new password using Android Device Manager we got an error message.
If you're looking to unlock the phone, there is no solution for this issue as of the writing of this post for Samsung Galaxy S6 phones and older. If you're lucky and your phone has a microSD card slot, you might be able to salvage your photos or files as they might have been saved there. If there is anything important on your internal device storage you're out of luck.
It's worth mentioning both Google and Samsung Support teams were unable to do anything about the situation even though we had full access to the Google Account and verfied ownership of the device with the carrier on a 3 way call.
Be wary of setting xkcd-esque passwords in Android Device manager.
For other services it is still generally a good idea to use long memorable passwords or better yet, use a password manager.