A "secret" hiding in plain sight.
What is obvious to you is not obvious to others. I recommend explaining and clarifying if you care about persuasion.
Pardon the cliffhanger style.
I have begun crafting an explanation, but not sure when it will be ready.
But when you recognize that thinking predates symbolic language, and start thinking about what thinking needs, you get closer to the answer.
A "secret" hiding in plain sight.