I've very often seen both and I use both randomly depending on my small
experience.

What is the grammar behind that?

For example:

人生の小さな瞬間

Why not 人生の小さい瞬間?
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2020-02-22T22:24:04.663
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2020-02-23T02:06:27.180
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question
grammar
When to use 大きい and 大きな?