In most cases, suspicion seems like the best defense of acting ambiguity-averse. However, suspicion does not support ambiguity-aversion in all cases. For example, as in the set-up to the Ellsberg Paradox, suppose you have an urn with 30 red balls and 60 black or yellow balls, with the balance between black and yellow balls unknown to you. You can flip a fair coin, and then draw a ball from the urn. You win $100 if either the coin lands heads and then you draw a black ball, or if the coin lands tails and then you draw a yellow ball. Otherwise you win nothing.
You flip the coin and it lands tails. You are about to reach into the urn when a casino employee, after glancing at the coin, interupts you and says “Wait! Of course you still have the right to play the game by the rules agreed to previously if you want, but I just remembered that I heard you are ambiguity averse, so out of the kindness of my heart, I’m willing to let you change the rules so that you win $100 if you draw a red ball, giving you a known 1⁄3 chance of winning, instead of if you draw a yellow ball, which gives you an unknown chance of winning in [0, 2⁄3].” To an agent following MMEU, this looks like a pretty good deal. However, you might be suspicious that the employee made that deal because ze knows that there are more yellow balls than black balls, and is trying to trick you into decreasing your chances of winning.
In most cases, suspicion seems like the best defense of acting ambiguity-averse. However, suspicion does not support ambiguity-aversion in all cases. For example, as in the set-up to the Ellsberg Paradox, suppose you have an urn with 30 red balls and 60 black or yellow balls, with the balance between black and yellow balls unknown to you. You can flip a fair coin, and then draw a ball from the urn. You win $100 if either the coin lands heads and then you draw a black ball, or if the coin lands tails and then you draw a yellow ball. Otherwise you win nothing.
You flip the coin and it lands tails. You are about to reach into the urn when a casino employee, after glancing at the coin, interupts you and says “Wait! Of course you still have the right to play the game by the rules agreed to previously if you want, but I just remembered that I heard you are ambiguity averse, so out of the kindness of my heart, I’m willing to let you change the rules so that you win $100 if you draw a red ball, giving you a known 1⁄3 chance of winning, instead of if you draw a yellow ball, which gives you an unknown chance of winning in [0, 2⁄3].” To an agent following MMEU, this looks like a pretty good deal. However, you might be suspicious that the employee made that deal because ze knows that there are more yellow balls than black balls, and is trying to trick you into decreasing your chances of winning.