Way back in the day when lines were first being painted on roads. The early lines were painted by hand. In those days, a painter was hired and given a stretch of road to paint. The first day he got on very well. In fact, he was one of the best line painters they had ever had. His lines were perfectly aligned, there were no unpainted areas in the space where there should be paint, and he managed to get 500 yards of road painted. The average line painter normally did 250 yards in the first day. The managers who had hired him were quite pleased.
Well, the next day, he came to work and set off on his task of painting the road. He still had another 500 yards of road to paint. And yet, for as fast as he was, he was only able to get 350 yards painted that day. Not quite what his managers expected given his performance on the first day. But still, better than their average painter, and so they reasoned to themselves, “Maybe he hit an extra hilly patch of road or some other unforeseen obstacle got in his way.”
Finally, the third day, he came in and finished the patch of road he had been given.