Lyric discussion by cmgonemad 

The line is "It's the law of diminishing returns." This is an economic law concerning employment. When firms hire employees, each employee produces a certain amount of output, or "returns." Each additional employee adds to this total output. However, it gets to the point where each additional employee crowds the workspace and hinders production, so that each employee is therefore able to produce less output for their wages. Therefore your returns begin to diminish if you hire too many employees.

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