What is a profound thought?

I’ve read the two previous fluther questions on the topic of “profound”, and I’ve looked up the definition. I still don’t get what constitutes a profound thought. Can a person decide for themselves that a thought is profound? Is it something that observers judge?

inspired by the discussion of the ‘invention’ of longitude by a ‘simple’ carpenter and watchmaker. He had profound thoughts and this enabled him to solve the problem of measuring time at sea. The longitude problem.