It does say something about the inverse though. If success is determined by positive thinking that seems like it strongly implies that success is a necessary a

It does say something about the inverse though. If success is determined by positive thinking that seems like it strongly implies that success is a necessary and sufficient condition. Which implies that a lack of success is a failure of attitude. Admittedly, this is mostly a semantics game of what specifically "determines" means, but to me it strongly implies both necessary and sufficient.