Wikipedia:

"his professor told him that, in order for him to get a C, the idea had to be feasible"

I had to do some searching to get the context here, so for anyone else similarly confused: http://en.wikipedia.org/wiki/Frederick_W._Smith

This (apocryphal) quote is attributed to Frederick Smith, who described an overnight shipping company as part of a paper for an economics class at Yale. He later ended up founding FedEx.