I really would absolutely not recommend getting a dog that has been "left behind".
Clearly you just hit unlucky though. Every single dog I’ve had (all ten of them since I was a child) has been ‘left behind.’ All KC - three ended up at crufts. All got between 8-10 weeks old. So unless you mean 20+ weeks, you should be careful of parroting nonsense.
Do you want to know why I got LOL? Because I specifically pick them. When I view the litters, I very often say I’ll take whichever dog is left. Why? Because by and large ‘last in the litter’ is an old wives tale. None of my dogs, bar one who developed neurological issues which couldn’t have been foreseen, have any displayed any negative behaviour.
Dogs get left for any number of reasons:
- not breed standard as puppies
- wrong sex
- boisterous
- to quiet
- just not enough interest in a litter
The ONLY reason to not pick a puppy that has been left is because it’s never it’s/fearful. And then I only say that to not experienced dog owners.
The reason my cocker spaniel who I showed for years was left and I got her at ten weeks? Female. No one wanted the bitch in a litter full of boys.
The reason I got my golden? To boisterous - no one wanted to take the puppy pouncing around being a plonker. Him now? 14 month, walks to heel perfectly and has done his SWCG.
Unless a dog is nervous or fearful there is no reason not to get the last pup in a litter