I remember an example similar to this from high school algebra-- when we had started learning about conic sections and polynomials. A barber's profit was modeled as a function of the price he charged per haircut. It turned out that the graph was an upside-down parabola. If he charged too much, no one would come and he wouldn't make any profit. If he charged too little, he wouldn't be able to cover his expenses, and he wouldn't make any profit. Our job was to find the function maximum in order to find what he should charge in order to make the most money. This article surprised me be cause it suggests the price-profit function is not only linear but horizontal over an interval. One possible explanation is that we don't have continuous data, and the actual function is some kind of complicated polynomial that has a lot of waves, which would allow a horizontal line to intersect the function at several points.