Sentence:  In such extreme conditions, the <WSD>Micawber Principle</WSD> that “something will turn up” to save the system is the only reasonable basis for action by businesses and investors, even if no one can predict exactly what "deus ex machina" will appear to save the day. 
Meaning of the word marked with <WSD> tags:  The claim that something good will turn up, especially when used to justify optimism.