Allegedly, it was given a lower grade due to it not being a feasible business plan, in the professor's estimation. Of course, this forms part of the legend behind Fred Smith and FedEx, so that should be taken with a grain of salt.
https://finance.yahoo.com/news/fred-smith-told-yale-professo...
Was the paper given a low grade because it was a bad idea or because Fred Smith wrote a bad paper? If his pitch didn’t work, did feedback from the professor help Smith sharpen his idea so he was in a better position to make FedEx a success?