What’s the worst puppy advice you’ve received so far?

I'm a force-free dog trainer in Brighton UK researching training mythology for a book project. New puppy owners get bombarded with outdated advice from trainers, breeders, vets, family, and that suspiciously confident person at the park.

What's the worst/most baffling advice someone's given you about your puppy? Bonus points if you actually tried it before realising it was rubbish.