千 (qiān): Thousand. In Chinese, large numbers like a thousand or ten thousand are often used to mean “many,” “a great deal,” or “completely.”
真 (zhēn): True, real, genuine. This is the core of the idiom's meaning.
万 (wàn): Ten thousand. This further amplifies the sense of scale and completeness.
确 (què): Certain, sure, definite. This adds a layer of confirmation and certainty.
The characters literally combine to mean “a thousand truths, ten thousand certainties.” This poetic hyperbole creates an overwhelming image of undeniable fact. It's not just a single truth, but a mountain of truths and certainties piled on top of each other, making the statement unshakable.