There are traders whose sole responsibility is to create alpha in only one sector or in one commodity group. Sometimes, it might be in just one contract such as natural gas, for example.
Since most markets are not trending, focusing on one sector can be a challenge if there is no direction or trend. Unless you've been trained...
These particular traders have learned to make money in natural gas regardless of the market environment. That ability did not show up overnight and it took a great deal of trial and error in order to understand the shifts between market environments.
You can get there also, but you have to be willing to run more than one system.
The key to understanding the context of "diversify" here, is that the trader deploys several systems depending on the market environment.
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When markets are trending, they're long or short. When volatile and choppy, they have vol crush trades on. When consolidating, they have credit vertical spreads. And when seasonal, they can create calendar spreads in futures. These aren't day traders either.
You can study the relationships between an underlying security and all the related instruments to find your trading edge.
Admittedly, some of them have access to the cash commodity markets too, so that gives them many more combinations of relationships to study.