As if this Russian roulette existence isn't enough, understudies also have to endure icy resentment when they finally step on stage, from audiences angry at being short-changed.
He dismisses the Hollywood myths about understudies seizing their moment, inevitably depicted by a shot of editions of Variety spinning towards the camera proclaiming the overnight discovery of a new star.
The reality is very different, says Chris. "There are plenty of good leading actors, but decent understudies are hard to find.
If anything, the Americans now find their former understudies too aggressive.
If there was any big conclusion to be drawn from tonight's impressive sparring by two understudies, it was that if Joe Biden and Paul Ryan can do it Barack Obama's dismal, passive performance last week in his first debate with Mitt Romney was all the more baffling and inexcusable.
And some non-radioactive elements are not perfect understudies for their hotter counterparts.
He had praise for some of his side's young understudies in defence, though.
At a net 56 seconds and over a kilometre ahead, Spithill and Ainslie, plus Australian strategist Tom Slingsby, became understudies in a command performance which may not have long to run.
But at his best – and he will have to perform at somewhere near the optimum to hold off his young understudies, Jamie George of Saracens and Luke Cowan-Dickie of Exeter, he is the nearest thing England currently have to a world-class tight forward.
The lack of control and penetration demonstrated by Finn and Broad's understudies – Warwickshire's Chris Woakes and Surrey's Jade Dernbach – means Cook will probably be keeping those fingers crossed for the next seven days.
Reserved occupations: Englishmen as understudies * The Football Association, whose plan to have English managers shadow Fabio Capello has yet to get off the ground, has a history of giving them experience with a view to them ascending to the national team job: Brian Clough Had a very brief spell as England Under-18 manager in 1977.
