The first thing we need to look at is understanding the breed, what are they bred for? German Shepherd is genetically hardwired to ORIENT->>eye->>stalk->>chase->>(Nip)
They are like a big collie, they herd things and act as a mobile fence around sheep. Their critical period of development is between 4 and 18 weeks during which time the brain volume increases to 80% of its adult size.