This has come up recently. If you do a search for singleton you will find plenty of comments ;-)
I have a singleton pup here. She is now 10 1/2 years old and a right pain in the neck :-D My fault, not hers, I hasten to add. Her mother rejected her, sort of. She would feed her and clean her, but then it was up to me to play with her. Mum didn't want to know. We took her everywhere with us, carrying her until she was innoculated. Was I glad when she could go down on the ground :-) She is very people friendly, but isn't so good with other dogs. She thinks they are all her best friend and doesn't understand when some tell her to get lost. This has caused a few problems over the years. She just didn't learn doggy etiquette. I now regret not taking her to puppy parties, or to play with other young puppies. They learn so much from their litter mates that we just don't realise. The main one being bite inhibition IMHO. I honestly hope you don't have a singleton. They are so much more hard work. :-D