A note on the birthday problem

Formal calculations often do not yield insight into "how your model solves your problem". A strategy in connection to the birthday problem is discussed that does give intuitive orientation. Furthermore some situations do not seem "stochastical" at first sight but can be structured by stochastical models. Even in these models do not fit the situation you can get sensible results from that models. The birthday problem is shown to be a problem of that type.