I think charbucks has the point: If I already know that there is something which will make me unhappy, than my happiness is already gone, and I can't shose to rather be happy anymore. So I guess the choice should really rather be, if you want to be happy, or rather know something which could or could not make you unhappy... so that on the one happiness side you really don't know!

Although I am not sure what to chose either then...