I think its the phrase "Blow up" that is the myth. An engine running poor fuel wont "Blow up" but it may damage the bore, rings, piston crowns and skirts, seals etc. Also the key word here is "May" , poor fuel isn't necessarily a death sentence for an engine but it is a little like eating sugar, tastes great but you know its doing you damage over time. The newer injected engines have finer tolerances and smaller timing parameters, putting them at higher risk of failure. In saying all that you would be amazed what a modern internal combustion engine can run on. Many moons ago when I did my apprenticeship the amount of things my fellow class mates and I poured down the carby of a running engine when the teacher wasn't looking, oh jeez here come the memories lololololol. Any who , its better to run fresh rather than stale fuel if you can.