A project is a set of interdependent parts that also sits inside larger systems — a program, a portfolio, an organization, a market. This principle asks you to take a holistic, systems view: recognize the interactions, evaluate how a change in one area ripples into others, and respond to keep the whole performing well.
In practice this means balancing inside-out and outside-in perspectives. Your deliverable will likely become part of a bigger system to realize its benefits, and external conditions keep shifting, so systems thinking is continuous — not a one-time architecture diagram. A small decision in one area, like a schedule change, often has outsized effects on cost, stakeholders, and risk.
Common misunderstanding. Systems thinking is not over-analysis or boiling the ocean. It is the habit of asking what else a decision touches, so you avoid local fixes that create bigger problems downstream.