Boeing is well aware of the problem with workers forcing things to fit the wrong way anyway, and take that into consideration, making it as hard as practical to do so.

For example, if the hydraulics are hooked up backwards, the controls are reversed, which is a disaster. So the design:

1. uses different port sizes for the input and output 2. one port uses left hand threads, the other right hand 3. the lines are physically not long enough to reach the wrong port 4. very clear labeling 5. inspections and signoffs