I do not believe that good PMs should know everything. They should be experts in leading projects, and may also be experts in certain technical subject matter categories, but not in every technical subject matter category that the project team encounters difficulties in. Matrix organizations have evolved (in part) to take advantage of the subject matter expertise throughout the organization, and PMs are expected to be able to effectively evaluate options associated with those inputs, and make or recommend appropriate decisions. Thus, a PM should really know how to ask the right questions. This is particularly true for complex and risky projects where “doing more with less” is a key goal, and the organization is partitioned into pockets of technical expertise (e.g., with a matrix structure). What are the right questions to ask? This is not a trivial question. It typically takes a fair amount of experience and “scar tissue” to become proficient at it. In my book “Project Risk Management: A Practical Implementation Approach” I’ve sprinkled in probing questions to consider for evaluating plans and assessing potential causes of unsuccessful project execution – to facilitate the risk management process and help ensure that project plans are thoroughly vetted and sound.