There is no original thought. Thought is a function of language. We learn language from each others, from our culture, and through time. We agree on the meanings of theses words, and they form the basis of every communication, either externally to the world our internally to ourselves.
What is original is the context within which the thought exists. No other person has had your exact experiences. You will make unique connections between each thought, filtered through the lens of your personal perspective. When you express your thoughts, you send them back out into the world, and each of us grows intellectually richer.