A decision on maximizing profit or maximizing the return on investment.

Uncertainties about applications  like dynamic  loading instead  of static loading, vibrations, wind speeds.

Uncertainties regarding materials and skills required in the manufacturing.

Changing economic realities.

Unfamiliar environmental conditions like very low temperature.

The available standard data on items like steel, resistors, insulators, optical glass, etc are based on statistical averages only.

Due to the inherent  nature of processes,  all compts have a tolerance  in design leading to the probability statistics by which assemblies’ capabilit y is assessed.