Take guns for example.
Left-handed people will have difficulty using guns if the shell throwing mouth turns to the right. So is the handle of the latch. Left-handers will have difficulty using AK47. Because you need your right hand to pull the bolt. It's hard to aim at this time. M 16 does not have this problem, because the bolt handle can be pulled with both hands. There is also the problem of center of gravity. The center of gravity of the gun should be above the hand holding the gun. But everyone's arm length is different. Therefore, in order to pursue accurate competition, it is necessary to adjust the length and weight of the butt stock according to competitors to adjust the center of gravity. In addition, it is necessary to avoid misoperation. Such as the orientation and fixing method of the magazine. If the magazine has no obvious direction, it is easy to put it backwards. Wait, many, many places to consider. It can be said that man-machine interface is the most important place to pay attention to in product design.