In the 1930s, industrial engineering (IE) was just evolving. Industrial engineers wanted to study the effect of lighting on assembly lines. In a famous study, they segregated an assembly line and increased the lighting. As expected, the productivity went up. Next, they lowered the lighting and the productivity went up even more. Then, they lowered the lighting until one could hardly see, and productivity continued to go up.

Question: What did the industrial engineers fail to consider in their study? How can you avoid a mistake like the one in this study?