Why do many material samples need to be tested before engineers draw conclusions about fatigue?

Engineers must test many material samples because fatigue is inherently statistical in nature. When specimens are tested at a common stress level, their individual lifespans vary, falling both above and below an average value.1

Because of this variability, designers rely on statistical theory to determine the necessary sample size to ensure data reliability. It is common practice to test several hundred specimens to account for these fluctuations before drawing firm conclusions about a material's behavior under fatigue.1