Assume I have two Github accounts, one for regular use and one for testing purposes. Or two PGP keys, one for pass and the other for encrypted email communication, and my backup scheme is exactly the same for both keys.
Now assume I use a single password for my two Github accounts and another single password for my two PGP keys.
To what extent is my overall security diminished by this practice?
This answer to a related question states that
you should never use the same password in different places, unless that password protects the same data or gives you the same privileges
In my hypothetical case, a single password would protect different data, but the threat model would be very similar.