Deb, yes very much so!!! It is very easy to "ruin" pulling for a dog especially when working with pups. IF you make a mistake that freaks them out bad enough they may never take to it. We had a problem like that with a pup at the kennel. We were running her with an experienced team (the only dogs fast enough for her) but halfway downt he trail there was a mix up (dunno what happened as I was not running them) and a fight broke out between the older dogs. By the time I got there with the snowmobile (not long which goes to show how fast something can go wrong) she had slipped her harness and was balking and straining and screaming trying to get away from the feuding dogs. We got everyone sorted out but when we went to hook her back up (I had tied her to the snowmobile) she flipped out and started shaking she was so scared. I took her back sperately and the rest fo the dogs and thier musher finished the run. She remained spooked for the longest time and was almost placed in a pet home as we didnt think she would come around from her traumatic experience. But luckily she would run with her brothers at least and we slowly introduced running with the older dogs again and now she's doing just fine!