A commonplace scenario is to be connected to your Mac via ssh and therefore not have the default keychain unlocked. The following occurs:

$ kopia restore sicp
ERROR open repository: get password: error getting persistent password: error getting persistent password: error retrieving password from OS keyring: exit status 36
$ security unlock-keychain
password to unlock default: 
$ kopia restore sicp      
Restoring to local filesystem ...

What would be nice is to change the ERROR printed to follow up with:
Try "security unlock-keychain" if you are logged in remotely.

Then I would be willing to wager that 9 times out of 10 the user's problem would be solved without the need to Google it.