Which troubleshooting technique can be used when the cause of an issue is unknown?

The technique of using "divide and conquer" is particularly effective when the cause of an issue is unknown because it allows you to systematically isolate and test different components or factors separately. By breaking the problem down into smaller, manageable parts, you can focus on one segment at a time. This structured approach enhances the chances of identifying the specific cause of the issue without being overwhelmed by the complexity of the entire system.

In contrast, relying on trial and error, while somewhat systematic, does not inherently focus on isolating factors and can lead to inefficiencies as it may involve testing combinations or making changes that do not necessarily address the root cause. The all-or-nothing approach lacks flexibility, as it does not allow for the incremental testing and isolation of symptoms, which is crucial in diagnosing problems effectively. Random guessing is the least effective method, as it does not involve any logical process and can lead to frustration and wasted time.

Thus, "divide and conquer" stands out as the most reliable technique for methodically narrowing down the cause of an issue when it is not immediately clear.