A prospective role candidate was blacklisted.
A prospective role quorum was blacklisted.
A prospective role candidate was already cast in another role.
A prospective role candidate failed the role conditions.
A prospective role candidate was not present for a role requiring presence.
A prospective role candidate violates an embargo.
The role at hand could not be cast in a way that would avoid failure while casting a downstream role (i.e., a descendant in the role-dependency forest).
The global conditions for the construct failed.
The casting pool was exhausted, but the minimum number of slots for a role were not filled.
The maximum number of slots for a role were filled, but there were outstanding precast candidates for that role.
The casting pool contained fewer candidates than the minimum number of role slots.
A precast candidate could not be cast in its associated role.
A candidate precast for a role is not included in the actual casting pool derived for the role.
A prospective role quorum failed the role conditions.
A member of a prospective role quorum failed the role conditions.
Enum specifying canonical descriptions for the possible causes of backtracking during role casting, which can be useful during debugging.