Birthdays are celebrated because we tell ourselves that the day so feted was the day on which we began to live. And indeed, it is from the day of our birth onward that our age is measured. At the same time, however, the majority of human beings proceed upon the view that our life in fact begins at our conception, some nine months before our birth – a view which would imply rather that it is our putative “conception day” that needs to be celebrated. We have to do here, then, with a “lie we choose to live by”. The truth lies somewhere between these two conceptions, even if not exactly midway between them: we began to live when our brain first achieved consciousness.