I walk up to a fully automated coffee dispenser and push the button to get an espresso.
What I do not know is that the button is connected to a device which consists of a radioactive source and a detector. The button activates the detector for 5 seconds and if it registers a particle from the radioactive material it will make an espresso and otherwise not (*). The probability to get my espresso, according to text book quantum theory, is exactly 50%.
But this raises the following question. There are many ways I can get the espresso, but there is only one way that it can fail. See, I push the button at 1pm, which here means I push it exactly at 1:00:00. Now the detector could register a particle at 1:00:01 or at 1:00:02 or ... at any time between 1:00:00 and 1:00:05. There is an infinite number of possibilities when and how the detector could register a particle.
But there is only one way it can not register a particle, with the detector shutting down at 1:00:05.
Since we all believe in the many worlds interpretation, this implies that there are many worlds where an espresso has been prepared and only one world where I fail to get it. So how can the probability be 50%?
Unless we assume that somehow the many different worlds are not equally real (x).
So perhaps the many worlds are not really real after all ?
(*) Actually, many automated dispensers in the real world follow a similar design.
(x) added later: There are proposals on how to save the appearances. Let me know if you find them convincing.