manufacturing deals with predictable and repetitive tasks, homogeneous delay costs, and homogeneous task durations. As a result, manufacturing sequences work in a simple first-in-first-out (FIFO) order. FIFO prioritization is almost never economically optimal in product development, because product development deals with high variability, nonrepetitive, nonhomogeneous flows. Different projects almost always have different delay costs, and they present different loads on our resources.
Donald G Reinertsen in The Principles of Product Development Flow