To me good breeding is the start of the jigsaw, then bringing on a pup and getting it out amongst everyday things progressing onto out coupled up on digs as it gets older, then when you think it's ready letting it go and hoping it has the drive, nose, determination etc. to see the job through until it's dug to is what makes a digging dog. I think a dogs upbringing bears a big resemblance onto how the dog will turn out as the final product, not saying all dogs make the grade but a good upbringing and confidence in it's owner helps a dog to be a better finished article IMO.