The event isn&#x27;t just &quot;there was a coin flip&quot;.  The event was &quot;there is a coin flip and I have been woken up&quot;.  For this event, two thirds of the time the coin flip will have been tails.<p>Halfers forget that there is an extra piece of information available &quot;I have been woken up&quot;.  SB knows that one third of the time she has been woken up it is because the coin flip was heads, and two thirds of the time it was tails.<p>Anyway, this is a stupid &quot;paradox&quot;.  It is extremely simple to build a simulation of SB being woken up and coin tosses, and if you do so, you get the clear answer - 1&#x2F;3.  There is no sampling issue or other trick that makes this simulation hard to write correctly...