Speaking of Pavlov, this exact tightening of a leash can lead to leash reactivity in a dog.

Leashes are a form of confinement for a dog, and without proper counter condition they can associate pulling or tightening a leash with negative feelings and can then apply those negative feelings to what they are seeing when pulling.

For example, you're walking your dog on a leash and your dog sees another dog and wants to be with them therefore pulls. Pulling feels restrictive and eventually starts feeling bad when it sees other dogs while on the leash. These negative feelings can turn into aggression.

The way to avoid this is to find a high value thing that can be used to redirect the dogs attention in these situations. Usually treats. When you have training time try other exercises like pattern games: place a high value treat 20 meters away, walk with the dog on the leash towards the item they want. If they pull say "oopsie" in a happy tone and walk back to the start. They only get the treat if they walk by your side all the way to the object. The dog will quickly learn the pattern and will get a great reward for following the pattern. With enough training and exposure to new distractions with positive reinforcement they will be able to walk by your side no problem. Only do this exercise if you're able to do it without stressing yourself or the dog. Also, don't take internet advice, it's best to get a trainer. Look for force free group training if your on a tight budget!