The law of diminishing returns is one of the most fundamental concepts in economics. It says: if you keep adding more of one input (like labor) while holding other inputs constant (like land or equipment), the additional output from each extra unit will eventually start decreasing.
Simple example: You own a small pizza shop with one oven. Hire 1 cook — output is 20 pizzas/hour. Hire a 2nd cook — output jumps to 35 (15 more). Hire a 3rd — output hits 45 (only 10 more). By the 6th cook, they are bumping into each other and output barely increases. That is diminishing returns.
This law explains why factories have optimal workforce sizes, why studying for 12 hours is not twice as effective as 6 hours, and why fertilizing a field beyond a certain point actually reduces crop yield. It guides business decisions about hiring, investment, and resource allocation.