The Medical Expert
The issue in a medical negligence action is whether the defendant deviated from approved or appropriate practice. It is an error, usually, to think that the plaintiff will succeed if he/she proves that there would have been no injury had the defendant followed a different course of action. (The exceptional case where it would not be an error would be one where the court was persuaded that the conventional practice carried such obvious defects that it was indefensible and where the court effectively condemns the defendant and the practice.)
There is also the question of talent. Commonly we “know�? what we have to find out, before we find it out. Fortune favours the prepared mind.