Hello my friend
Thank you is indeed a great virtuous word needed to be said in our society. You cited instances in which thank you can be said, in cases where you are in an accident and get rescued, try to say thank you, and also after being aided in an examination, endeavor too to say thank you. It would benefit the society and make our society a better place to be in. It is best to say thank you as it would make us show appreciation to our helpers. Success in the challenge my dear friend