Reprimands should communicate that the dog is misbehaving, and are best when they also tell the dog what to do instead. You certainly needn’t hurt the dog, but you must communicate that you are upset with them and you mean business.
An effective trainer can switch immediately from sweet praise to stern reprimand. Use the tone of your voice to let your puppy now when you like what they’re doing and when you don’t.
Dogs can’t speak English, so effective praise must be in an enthusiastic & energetic tone of voice. If you can’t praise your dog, you’ll never be able to train them.
The most effective reprimands are short and startling. A single, abrupt correction is much more effective than repetitive corrections that become gradually more severe.
This poor volunteer illustrates how frustrating and upsetting it can be to not know what is expected of you. However, with a little luring it’s much easier to communicate what you expect of your training subject.