So what really is the deal with the iPhone Encrypted Backup Password?

I am one of thousands of people, apparently, who have been screwed over by the iPhone encrypted backup password debacle with apple.

See: https://discussions.apple.com/thread/5597871?sortBy=upvotes&page=2 (and other support threads you can google)

I literally just setup a new "secure password" that I changed all my important passwords to (iCloud/Apple ID, etc) preparing for some international travel. There is no way in hell that I didn't select this same password when I entered a password to encrypt my latest iPhone backup on Sunday.

To my shock, it doesn't take when I try and restore. Now I've tried about 34ish passwords from my past 10 years and variations (no caps etc) and nothing.

WHAT is the actual deal here? In the discussion thread linked above, people have literally given every random answer under the sun but it's still not understood how this works?

(I entered what must have been all of my past Apple ID passwords, still nothing).