For the non-pilots:
Boeing Quick Reference Handbook:
While every attempt is made to supply needed non-normal checklists, it is not possible to develop checklists for all conceivable situations.
In some multiple failure situations, the flight crew may need to combine the elements of more than one checklist. In all situations, the captain must assess the situation and use good judgement to determine the safest course of action.
The Flight Crew must be aware that checklists cannot be created for all conceivable situations and are not intended to replace good judgement. In some situations, at the Captain's discretion, deviation from a checklist can be needed.