An unknown exception was thrown when the command was being run
The user wanted to exit the REPL
Failing results never call their callbacks, and just remain unchanged
A known failure occured, maybe caused by an exception (e.g.
is any exception that caused this known failure; currently only used for the "Interrupted!" failures caused by Ctrl-C
the message we want to display on screen due to this failure
Successes map and flatmap just like a simple Box[T]
Nothing was entered