Establishing well-defined objectives and success criteria is essential as outlined in the OSS TMM, which emphasizes a structured approach to testing. This ensures that the test will meet the specific goals and that the results can be measured effectively, leading to consistent and repeatable outcomes. Answer 'Automating all test procedures' is incorrect because while automation can be part of the process, it does not guarantee that the testing objectives are well-defined or that the success criteria are established. 'Conducting covert testing without informing the IT department' does not adhere to best practices for responsible testing and could lead to legal and ethical concerns, and thus, does not align with the OSS TMM's emphasis on structured and authorized testing. 'Focusing solely on high-impact vulnerabilities' may lead to a narrow scope that overlooks other important security aspects and reduces the testing effectiveness.