The dog who can, without upsetment, without fear, without signs of nervous tension, flight reaction, worry, whining, etc., accept its entire universe all of its environment with every characteristic of heat, cold, noise, population, surprise, etc. is a dog of strong nerve. Nerve is a sine qua non for the working dog. The canine nervous system provides the deep inner core of calmness and confidence upon which all the working dog's strength depends. Without it, there can be no reliability in work and no matter how much training is put into the dog; it will not be a great working dog if it lacks steadiness and soundness of nerve.
The nervous system of a young pup may be evaluated early in life, long before it is required to face a changing environment which might be frightening and is often full of surprises. However, the final judgment on a dog's character cannot be made before all of its components have matured into a solid functioning system. The solidity of a strong nervous system is the puppy's first defense against the challenges life will place in its path. Nerve is the ability to roll with the punches. Unexpected changes in the pup's environment will not shake its calm and youthful curiosity if these are housed in a strong nervous system to begin with. Loud noises (thunder, fire engines, gun shot, etc.) do not make it cringe, whine, or run for shelter. As it grows, the puppy with sound nerve will emerge as a confident dog, willing to please its owner. Panic it unknown to this dog and fear does not bring a bite reaction. Nerve is the critical factor in working dog temperament.
Because of its significance in the whole working temperament, no excuse should be tolerated when it is lacking. A dog without nerve or with weak nerve should just not be bred. Neither should such a dog be forced to work when its basic constitution has not fitted it with this necessary requirement. A dog with poor nerve should be allowed to live its life as a pet in a non-threatening environment.
Breeders who deliberately breed weak-nerved animals (because they are pretty, because they have a nice top line or super angulation, because they have a proper tail set, etc.) are selling short the future of the breed. Even a superb physical specimen of excellent conformation, coat and color should be rejected for breeding if it exhibits the signs of a weak nervous system.
All dog activities, whether in show or sport, should include an evaluation of the nervous system with disqualification from further participation when nerve is not sufficient. In Schutzhund for example, there are several tests for the dog's nervous system early in the trial - the pretrial temperament test and the gun shot test. The Schutzhund prospect must be gun sure. Walking in obedience, the dog is let on through its routine while a gun is fired about fifteen feet away. If the dog fails to be gun sure, if it reacts with weak nerve, the judge will either test it again or simply disqualify it from further participation. Similarly, all screening of good dogs should take the nervous system into serious consideration for without it, the animal will never develop its work, show, or breed potential properly.