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If the only choice was between possibility 1 and 2 you would happily put it all in pre-flop. The threat of possibility 3 is the only reason to stop raising.

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Yes of course this is true. Even getting 2.5:1 on your money is a huge edge. So I guess you're right that the AA possibility is limiting the preflop raising. But I also do think that the possibility of an ace on the flop is tremendously important. To put it in a NL context, how many people would ship it with KK preflop, assuming reasonably deep stacks?