Two of mine are exactly the way their temperament testing and the input of the breeder would have led me to believe when they were young puppies. Of course, One is a 7 year old now, and while he still plays, he's not the "busy boy" puppy he was. The other that hasn't changed much is my youngest girl, who at 14 months is still very much a puppy, very driven, very smart, needs to be "doing" things, but still VERY sweet and cuddly when she winds down too.
The middle girl is the one who changed, though looking back, there were signs of "who she would be". During temperament testing, and when I first spent time with her, she was the first to explore everything, very people oriented, very food motivated, lots of play drive, great natural retrieve. But there was also little to differentiate her from her sisters, who were also great puppies. She is STILL all that. She is, by far, the most athletic of my three and the smartest. That intelligence has been a two edged sword, however. She is what is known as a "single trial learner". She assesses things, figures them out and does them. Done in one. That also means she can learn the wrong thing very quickly too.
The PROBLEM is that a puppy like that can also learn the WRONG things during her "fear periods". Pixel got charged twice by large black pit bulls when she was a puppy. In both instances, I had no choice but to yank her off the ground by her harness to keep her from being eaten. The result is that we have gone through a VERY long period of her being terrified of big black dogs in particular, and large dogs in general. To the point that we couldn't even take her to our training center, because she couldn't work there. It has taken ALL my patience and over a year to get her back to where she is solid at the training center, and able to work through encounters with big dogs on walks. We are still VERY careful with orchestrating positive interactions for her, and we work EXTREMELY hard to make sure she doesn't experience any other big dog problems.
None of the above affects her much as a house pet. She has always been a darling, and gets along tremendously well with my other two. In fact, part of her "therapy" as been going on walks with dogs she knows well and who are solid around other dogs. In the late fall, we were at a campground on a weekend that was having a "Halloween theme", and there was trick-or-treating for the kids. Not only was the campground packed with kids running around in scary costumes, but many of them were walking large DOGS in scary costumes. We were out on a walk, and I had my three and my friend had her two whippets. Pixel moved herself into the middle of the group of dogs, then trotted along, as happy as could be, tail in the air. "Tail down" means she is frightened, and we've actually taught her to cheer up by saying, "Where's your tail!?!" Obviously this wouldn't work if it was something terrifying, but if she's just worried, she usually shakes it off, the tail come up and we're off again.
So this is where "nature" and "nurture" come together. I chose a puppy who SHOWED that she was an extremely quick learner, AND showed some signs of having trouble recovering from a startle. No puppy is perfect. She has a tremendous number of positive qualities. We were very unfortunate that she had two really scary incidents at very poor times in her development. Another puppy might have just brushed these encounters off, but because of her natural tendencies, it took a LOT of work for us to get through them. We love her to pieces, and were committed to putting that work in. For a lot of people who are not interested in performance sports, this wouldn't have made any difference at all. In my case, I have had to change course with her. Although "never say never", especially considering how smart she is, I am concentrating on the other two for competition, and she is our adorable house pet, who is the apple of her Daddy's eye.
If she comes around to the point that she is comfortable enough around other dogs that she can compete, that would be great. But we won't push her.