When I make a Database Master Key for a database:
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'Some Long Password'
This page from Microsoft recommends I back it up offsite:
I've confirmed through testing that the Master Key is stored when you backup the database. I'm already backing up the database, and I'm already storing the password safely. So why do I need to backup the Master Key too?
(As an aside, I am already backing up the Service Master Key and storing offsite).