Safety Factors Scale with Uncertainty

A safety factor is the ratio of the load a structure can actually take to the load it is rated for, and its size tracks two things: how well the material and loads are known, and how bad failure would be. An aircraft part made from a well-characterised alloy and inspected constantly may run at about 1.5, while a lift cable runs at 4 or more. Higher is not automatically better, because every additional factor costs mass and money, and in an aircraft it costs fuel for the whole life of the machine.