The external expression of poetry is very important in meter. Sometimes reading poetry is catchy because it conforms to the rhythm. I also like to write poems, but I didn't pay attention to the meter before, so the poems I wrote are a bit awkward to read, with bad breath, without the flat rhythmic beauty and endless aftertaste.
Therefore, poetry pays attention to meter and has a strict format. But more strictly speaking, the poems before Tang Dynasty are called classical poems, and the poems after Tang Dynasty are called modern poems. Classical poetry generally has no metrical requirements, while poems in the Tang Dynasty and beyond have strict metrical requirements, especially quatrains. There is a fixed sentence pattern, where it is flat, how to use rhyme, and there is a book to look it up.
The words are all the same, and there are formats. The predecessors have already had a character spectrum, so you can learn to write according to those.
But it doesn't mean that we must strictly follow the rigid format. Flexible. Words don't hurt meaning, which is also a rule of poetry writing. You can not follow the correct format, but it is definitely not a complete failure rate. For example, Li Bai's Thoughts on a Quiet Night is memorized by everyone, which is not completely in line with the rules, but it is not completely out of line. Therefore, poetry, whether ancient or modern, must conform to the rules and have a fixed format.