question:  Why does Simon ultimately deny Mr. Oyster's request to go to Oktoberfest?
context: He looked over at Betty and said, almost as though reciting, "What I need is a vacation." "Providence," Simon told her whilst fiddling with the aspirin bottle, "will provide." Simon said unenthusiastically, "Good morning, Mr. Oyster." When Simon continued to say nothing she ventured, "Time travel is impossible." "Then you'll realize that there are a dozen explanations of the paradoxes of time travel. It's my contention that within a century or so man will have solved the problems of immortality and eternal youth, and it's also my suspicion that he will eventually be able to travel in time. Simon seemed incapable of carrying the ball this morning, so Betty said, "But ... Mr. Oyster, if the future has developed time travel why don't we ever meet such travelers?" "The usual explanation, Betty, is that they can't afford to allow the space-time continuum track to be altered. Mr. Oyster returned his glasses to their perch, bug-eyed Simon, but then nodded. Simon said, "You want to hire me to find a time traveler and in some manner or other—any manner will do—exhort from him the secret of eternal life and youth, which you figure the future will have discovered. The Oktoberfest is one whale of a wingding." You could be a four-armed space traveler from Mars, and you still wouldn't be conspicuous at the Oktoberfest . You can take the plane to Munich, spend a week there and—" Simon was shaking his head. Mr. Oyster was taken aback himself. It goes like this:" I got a thousand dollars from Mr. Oyster (Simon began) in the way of an advance, and leaving him with Betty who was making out a receipt, I hustled back to the apartment and packed a bag. It takes roughly seven and a half hours from Gander to Shannon and I spent that time dreaming up material I could put into my reports to Mr. Oyster.
output:  He knows he will not be allowed to do something that might impact the past
options:  He believes that Mr. Oyster is on a mission to destroy time travelers  He thinks that Mr. Oyster is attempting to alter the space-time continuum  He knows he will not be allowed to do something that might impact the past  He does not believe that Mr. Oyster is offering fair compensation