You take your dog to classes, spend thousands on trainers, and he still chews the sofa and shits in your slippers.
What if you had the training method in your pocket all this time? The secret is not in severity, but in... cheese.
Yes, regular cheese that will turn your stubborn person into a genius in three days.

Here's how it works: Cut some cheese into fingernail-sized cubes. Hide a piece in your hand and say, "Sit." When your dog sits (even by accident), give him a treat and praise him enthusiastically. Repeat 10 times during your walk.
On the second day, he will sit on command without coaxing. Why? Cheese activates the pleasure zone in his brain, and he will associate obedience with joy.
The second trick is the "three-second rule." If the dog does something forbidden (like jumping on a guest), you must say "No!" within three seconds. Later, he will no longer understand why he is being scolded. And never hit him - this only teaches him to be afraid, not to obey.
The third secret is fatigue. Is your dog chewing on furniture? It's not being naughty - it's bored. Before leaving for work, play "search": hide treats around the apartment. Spend 10 minutes, but the dog will be busy for an hour. A tired dog is an obedient dog.
And lastly, forget the word "no". Say "Give" instead of "Don't touch", "Place" instead of "Go away". Dogs don't understand negatives - their brains fixate on the last word.
Want your friend to be perfect? Stop trying to change them and start understanding them.