I agree no one can "predict" but a guy can dang sure put the odds in his favor by doing his homework on the pedigrees and ancestry of the dogs. Find a family of dogs that have produced what you need over a few generations and breed dogs that stack as many of the ancestors that suit your needs and you'll be surprised what you can accomplish. To many folks get caught in breeding best individual to the best individual and neglect to pay any attention to the ancesty. The dogs will likely breed more like whats behind them than they do themselves. JMO
I agree...the hardest part about starting a line of dogs is finding a family of dogs that will get you started in the right direction...
but I will add that I will do all I can in picking the best pups as I see it at the time...one can not always keep the whole litter...so what I do is test the pups and might cull the obvious at 6-8 weeks, keep 6 pups to about 16 weeks of age and cut one more at 6 months and more than likely what I keep after that will make good dogs but only the best of the 4 remaining will get breeding privileges...sometimes of those 4 I will keep 2 if that was all I needed...but it is well worth the expense in doing it that way...
as the line is developed we will see a higher percentage of keepers per litter...and they culling bar can be raised...I call it purifying the gene pool...the cream rises to the top...