In some applications, simple things such as grounding the external connectors to the chassis can considerably improve the overall ESD performance because it allows some of the energy from the ESD strike to dissipate directly to the case and not reach the main PCB. One can also minimize the case openings or number of holes in the product enclosures to prevent the ESD strikes from reaching the active circuitry. Take a look at the diagrams on the screen to get a better idea of this.