When working with pressurized liquids and gasses it is critical that specifications are made properly to ensure positive sealing of all connecting elements. While there are a number of suppliers that promise interconnection technologies, they are not able to guarantee that the integration with other subsystems is done properly. It takes experience to know which interconnects are reliable, available, and easy to work with.
I've learned another important issue with pressurized systems is quality control. Pieces need to be manufactured to spec, be finished properly, and most importantly assembled properly to ensure functioning seals. Any single non-functioning component can lead to a difficult process of chasing down the source of the system problems. This is generally not a great use of anyone's time.
Safety. When working with highly pressurized fluids and gasses there is the potential for a sudden release of energy. Careful discipline in placement of components, valves, and pressure regulators can help minimize the risk.