you can identify the faults by noise/smell/feel/taste/vibration frequency through your arse before you need to go and sign the boxes of lies out of the HES.
When the J/T lends you his Gen book and it has more in it than the fiche room.
When you have to do a running decu reset on the Q jet while it's waiting to taxi.
When you come back from anywhere knowing the pigs can't get at the duty free stash as its locked up in the crypto lacon or stuffed in the pylons