Since other investors may be smart, well-informed and highly computerized, you must find and edge they don't have. You must think of something they haven't thought of, see things they missed bring insight they don't possess. You have to react differently and behave differently.Out of the main four edges that an investor can have, namely i) information, ii) analytical, iii) knowledge and iv) time, here Marks is talking about the analytical or insights edge. With the same set of information, can you have better or different insights which will result in a differentiated result for your portfolio.
To achieve superior investment results, you have to nonconsensus views regarding value, and they have to be accurate.
For your performance to diverge from the the norm, your expectations - and thus your portfolio - have to diverge from the norm, and you have to be more right than the consensus. Different and better: that's a pretty good description of second-level thinking.
I think this is the simplest yet most overlooked part. You cannot get superior results by doing what everyone around you is doing. Some investors I know of surround themselves only with people who have very similar viewpoints about life and markets. To me, they are living in an echo chamber. To really have a nonconsensus view, you have to actively look for disconfirming evidence. That is, an idea which is exactly opposite to the one you hold.
As Charlie Munger has said, " It's bad to have an opinion that you are proud of if you can't state the arguments for the other side better than your opponents."