It's plain as day
Meaning
It means something is extremely clear and easy to understand.
Origin
The phrase "plain as day" taps into one of humanity's most primal experiences: the profound clarity and visibility that daylight brings after the obscurity of night. For millennia, before artificial lighting, the transition from darkness to day was a daily revelation, making everything clear, obvious, and unmistakable. This universal understanding of daylight as the ultimate state of clarity naturally lent itself to a powerful idiom, evolving to describe anything that is undeniably clear and easy to grasp, just as the world itself becomes under the bright sun.
Examples
- The instructions for assembling the bookshelf were so clear, it was plain as day what I needed to do.
- After she explained it again, the solution to the math problem was plain as day to everyone in the class.