The only problem is, once you are not expecting to be hanged, you realise that this is the exact time you will be hanged. Being thusly expectant, you will not be hanged, which means this is the exact time you will be hanged, etc.

Of course, the execution will then take place as it had been planned all along, but you will be so distracted by the above circular reasoning that you won't actually be expecting it.

However, with this in mind, you will be expecting it, thus stopping the execution, but also creating another layer of circular thought to be distracted by, allowing the execution to go ahead again.

Of course, you know this, and thus layer after layer of this pointless reasoning goes on and on into infinity, occupying so much of your mind that you get hanged anyway.

But! You realise this! (and so on...)