The obvious rebuttal is to argue that there is a pattern to picking unicorns, and then argue that a current investor will beat the market this year, and then u

The obvious rebuttal is to argue that there is a pattern to picking unicorns, and then argue that a current investor will beat the market this year, and then use the same argument next year. Note, being a unicorn isn't necessarily a sinker for an argument, it just can't be your only defence (i.e. gravity is the unicorn of theories about why things fall :) )