It relies on the parties to take an action (that they are both incentivized to take in order to see if they won). This is similar to atomic swaps - they setup a

It relies on the parties to take an action (that they are both incentivized to take in order to see if they won). This is similar to atomic swaps - they setup a time boxed window when people must take an action. If one of the parties fails to act in time, they will, in fact, lose their coins.