It's about as close to an impossible job as you can find in football.
On Saturday night, in front of an audience of millions watching live on BBC One, League Two Cheltenham Town will confront the might of Manchester City and their master manager Pep Guardiola in the FA Cup.
A famous occasion for the minnows, undoubtedly, but surely not a match they can actually win?
Or so you might think. Cheltenham have a secret weapon - a group of former Royal Marines Commandos whose day job for 10 years was to redefine what impossible means.