I think the breakdown in this argument is the fact that $Y is not the same for everyone. > $Y is the net present value of all future earnings. First of all, ‘

I think the breakdown in this argument is the fact that $Y is not the same for everyone. > $Y is the net present value of all future earnings. First of all, ‘future earnings’ is a time-dependent probability distribution and this means that the outcome is not certain at the time of transaction. For example, we can imagine that a particular stock has a 50% chance of tripling in value after 10 years and a 50% chance of going bankrupt. What is the current value of this stock $Y. Even in this contrived case it seems like different people could value this stock differently today even knowing the probability exactly. Some investors need a reliable fixed income from their investments but don’t care much about growth (for example some retirees). They might not like this risk. Other investors want to increase their capital and are willing to risk volatility and losses. There are some cases where there is a clear zero sum game (pump and dump schemes for example), but I don’t think this is true for most transactions.