You need to have a clear answer. Edge has to be quantified. If you don't know what your edge is, there is a good chance your counterparty who you just traded with does know.
Totally agree. It has to be quantifiable; but you also need to watch out for the erosion of the edge. Also, even if you have a quantifiable edge, you also need to understand the underlying reason for which the edge is manifesting - if possible. And there lies the rub.
For derivatives, possibly theta, gamma.. etc. Arguable either is an edge; and maybe neither is. Forecasting - either price or volatility; but most forecasting and any modeling is again very prone to failure due to modeling constraints. So in the end its not such a simple answer - but a very good question.
