[tjradcliffe]

Reality is continuous. Human categories--like cancer--only have sharp edges because we draw them with an act of selective attention. The edge of our attention is discontinuous. Nothing else (that doesn't involved quantum mechanics or integer counting of attentionally-isolated objects) is.

"Cancer" is not a simple thing. Two people with "breast cancer" may have very similar or almost completely different diseases. As others here have pointed out, the magnitude and frequency of wins and losses matter even though trades are binary win/lose (which they can be because we've created an entire category of imaginary objects called dollars that can be counted).

Bayes rule is as applicable to any area of significant uncertainty, including win/loss magnitude. It is universal.