The thing that made Stevie unique, and drove coaches nuts, was his non-standard way of running routes. He always got to the spot, but he took a unique path that wasn't on any route tree (which is why Revis couldn't cover him). Fitz was smart enough to figure that out, which is why he and Stevie made such a great pairing. Fitz could always find Stevie open, wherever he was on the Stevie route tree. It's also why Stevie's career didn't go too much longer after he left the Bills. Stevie was a very good WR, but he needed the right kind of QB to take advantage of that very unique skill set.