Actually, raskerino, this is an excellent point, and I think you are dismissing it far to quickly. For one thing, Yu Yevon was originally just a summoner, remember? He manipulated an aeon into Sin. But what one person can do, another can reproduce. Sin can return, even without Yu Yevon. What's more, Sin usually did remain gone for longer than the mere two years that it has been since Yuna defeated him. It's almost strange that people would be so accepting of the "Eternal Calm". They've been living with Sin for a millenia, then all of a sudden someone defeats him and lives to tell the tale, and they just accept that this person has done what a thousand years of summoners could not, even though there is no evidence that Sin won't be coming back? No one is skeptical?