Good point. Yep it sure would be nice if every drug worked out, every project was wildly successful, every new hire was a wonder-kid, every investment only went up and to the right. That would make all the math so much easier wouldn't it?
Also the cost of drug discovery, which in this case amounted to some doctor suggesting let’s mix those previously approved drugs and see what happens, compared to 5–10 years of research, failures, and systematic work by chemists and biologists before any doctor is even involved.
...or the industry refusing to research a drug because of expense estimates!