You are being unfairly downmoderated. It is of course not a given that modeling economic systems is impossible, but there is considerable debate as to e.g. what degree prices are random/unpredictable. Everyone agrees the problem is extremely difficult, and it seems somewhat unlikely that there would ever be such thing as a universally applicable financial model. So the remaining question is, of course, to what degree are these models useful? I do not believe there is sufficient evidence to reject the idea that the models are of no utility, especially in the context of failing to price in risks. The contrary position is equally viable, and I would hope anyone with what they considered to be a knock-down argument would do more arguing than knocking down.