Let's analyze the sheer poetry of LWJ's famous line:

天天就是天天
usually translated to: Everyday means everyday.

天天 is an emphatic way to say "everyday." It literally means "dayday" by way of repetition, evoking the meaning of the word in its structure. +

Another way he could’ve said it would be 每天, which more literally means “each day”.

天天has a cyclical rhythm to it that is comforting, gentler, and sentimental. It is the poetic version of “everyday,” not rigid or tied to the calendar the way 每天 is.

A symmetrical way LWJ could’ve expressed “Everyday is everyday” would be, then, 天天是天天. This would be a nice equation. Dayday is dayday.

But there’s that 就 there that throws off the symmetry of the statement. The 就 does so much poetic work too +

就 jìu is a really complicated character with many meanings, but paired with 是shì (the verb meaning “is”) it serves as emphasis. 就是 is not just “is”—it means “precisely is”, “exactly is”, “even.”

He is saying cheekily that “everyday is exactly everyday.” +

But in saying 天天*就*是天天, however, LWJ is troubling this exactitude, throwing off the symmetry! Why this repetition “dayday is dayday” with a caveat variation?

I think the poetry of this line is that MDZS is a story about second chances and re-reading (the past, each other, ourselves). In WWX’s second life, he comes to learn that LWJ doesn’t hate him, doesn’t judge him—that LWJ loves him and that he loves LWJ.

The first 天天 and the second 天天 are the same but different. Wangxian are both the same but different. Each day they spend together will now be same but different.

LWJ in context is talking about having sex, but this sentence carries so much narrative weight/resonance! +

The 就是 affirms their happily ever after across timelines, promising a futurity.

天天就是天天 carries w it the promise of the comfort of everyday, of ritual and repetition, with an emphatic difference. That is, the comfort of mutual understanding and the rhythm of domesticity.

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