An interesting point. If a Captain is tired then I'd suggest the 'error' has already occurred.
Of course, we still need to manage the error and it's ongoing effects but it's not a threat.
To be technical too, if I'm tired on descent, the appropriate way to manage that threat is to 'rest'. I can't actually mitigate my tiredness by rest on descent can I.
Of course, we all know that when tired, what actually occurs is that our error rate will increase and our ability to trap errors will also decrease. Is that a threat? The error may be flying into a turbulent area with pax and carts still out. The error was lack of vigilance when ATC reported turbulence on descent because someone was so busy talking about all the stupid threats that people dream up to fill the briefing time.
