Learning
In each phase of my career when I took on a program management role, I reached out to the experts on the team to learn more in-depth about their fields. When leading a multi-national effort on multi-chip modules, I had hours-long sessions with a senior engineer to refresh my memory about signal integrity and packaging issues. When pushing new standards for high-speed interconnect chips, I had many, many lessons from analog engineering about PLL design, and with digital engineering about encoding techniques, encryption, pipelining, etc. Most recently, leading a project to produce test equipment, I dug into the software design with the help of the programming team to discuss partitioning the code, overlays, call-backs, compiled versus open source issues, etc.
In all of these cases, my involvement as an engineer with each team went above being the program manager, and generated a lot of trust and confidence both for them and for myself.