If we accept the exponential waiting time model, then another term for this phenomenon is Poisson clumping: http://en.wikipedia.org/wiki/Poisson_clumping http:/

If we accept the exponential waiting time model, then another term for this phenomenon is Poisson clumping: http://en.wikipedia.org/wiki/Poisson_clumping http://en.wikipedia.org/wiki/Poisson_clumping. I think one intuitive way to explain it is if you're flipping some biased coin continuously, then if someone walks in, you are more likely to currently be in a long streak and have stuff clump afterwards. For exampling flipping a coin with probability 1/60 of heads each minute for an hour (so average wait time should be 10 mins): > ''.join('H' if random.randint(1, 10) == 10 else 'T' for i in xrange(60)) 'TTTHTTTTTTTTTTTTTTTTTTTTTTTTTTHTHTTTTTTTTTTTHTTTTTTTTTTHTTTH'