One day when I was a junior medical student, a very important Boston surgeon visited the school and delivered a great treatise on a large number of patients who had undergone successful operations for vascular reconstruction. At the end of the lecture, a young student at the back of the room timidly asked, "Do you have any controls?" Well the great surgeon drew himself up to his full height, hit the desk, and said, "Do you mean did I not operate on half of the patients?" The hall grew very quiet then. The voice at the back of the room hesitantly replied, "Yes, that's what I had in mind." Then the visitor's fist really came down as he thundered, "Of course not. That would have doomed half of them to their death!" God, it was quiet then, and one could scarcely hear the small voice ask, "Which half?"
I worked for several years as a leader of birding tours, and I have met a few sad individuals who were so focused on adding to their life lists that they would refuse to look at a bird species that they had seen before, no matter how spectacular the view or how fascinating its behavior of the moment might be. “I don’t need that bird” was their standard reply.
For a person just getting started in some area of natural history, and unabashed focus on list-chasing is a good thing, at least for a while. The trick is knowing when to stop.
Keith Brown described how he got the idea “that the maximization of daily species lists of butterflies, a seemingly unscientific goal (though much employed in a sister area, ornithology), could give a large scientific fallout."
For example, he described how six weeks’ effort in the Brazilian central plateau had turned up twenty-five species previously unknown for the area—but then he had adopted the “maximization” method, and in another six weeks, he had found nearly three hundred more species.