1. (a) That's right. An agent has a duty to carry out the principal's instructions personally, especially if the tasks entrusted to an agent involve a degree of personal confidence in the agent, or an exercise of personal discretion by the agent. In such circumstances, the agent is not entitled to get another person (a sub-agent) to perform those tasks.

In the present case D's personal judgement as a specialist was required to evaluate the quality of the backup system and D should not have relied on an assistant to read and assess the documentation.