"The successful market participants I know have spent a great deal of effort thinking about–and researching–a unique approach to trading and investing that captures an enduring bias in the market place."
There are a few very important concepts here.
1- Spending effort thinking about a unique approach
2- Research that unique approach and refine into a tradable strategy
3- Focus that effort into finding an enduring bias in the current market place
You should use these guidelines to find a suitable trading edge. Ask yourself questions. Go look for the answers.
Another key point here is the word "Bias". From the dictionary,
a particular tendency, trend, inclination, feeling, or opinion
So, in other words a bias is also a definition of an edge. A trading edge does not work all the time. It is really a tendency for the market to behave in a certain way in a particular condition. If these conditions are met, the market tends to... That is an edge.