During weeks eight through twelve, there is a period called “The fear imprint period”. During this time any particularly scary or painful experience will leave a long lasting impression on your dog rather than if it occurred at any other time in his life. If the experience is very traumatic, It could literally ruin your dogs life.
While in this time you should avoid exposing your dog to traumatic experiences. For example surgery such as ear cropping, if it is going to be done then it should be done before 8 weeks or after 11 weeks of age. Also when you take your dog to the vet have the doctor give him a treat before he does any examinations just to make the visit to the vet a pleasant experience. Although you should stay away from any stressful situations, continue to train your dog in a positive way.
During his first year of growth you may see fear reactions at times. Do not respond by dragging him to the object that he was scared of. Actually do not reassure him or pet him. The reason for this is because he might think that you are encouraging his reaction and behavior.
What you should do is distract the dog with another toy or a treat to get his mind off of the object that scared him and on to something pleasant. Practice some of the commands that he has already been taught so he can focus on a positive experience. After about two weeks or less that fearful behavior will disappear.