I would define "success" as you've described as the combination of cross discipline work and market forces which produce a desired outcome. Having good design

I would define "success" as you've described as the combination of cross discipline work and market forces which produce a desired outcome. Having good design however doesn't depend on market outcome. You can have good design where noone is using it. I would say that good design requires cross disciplinary skills or knowledge - requiring a core set of "design skills" plus an understanding of psychology, the end user and the domain it's for. The successful emergent outcome of this is "good design". The difference between math and subjects such as design or stock trading is that math isn't judged by humans or human behaviour. Design will at the end of the day be judged as good or not by the people that interact with it. Stocks will be judged based on whether others are buying or selling. The skill in these things is predicting human behaviour, following patterns and managing risk. That's why in design it's a good idea to meet your users, and to iterate following rounds of user testing.