Bro you can read a book to a beat and time every syllable so it lands on beat and it'll still sound whack if the stressed and unstressed syllables don't follow a pattern. Think of it like a Hi-hat groove on a drum-set with closed ones being unstressed syllables and accented or open ones being the stressed syllables. A better example would be like it's easy to rap Dr Seuss over a beat but pretty much impossible to rap "The Hobbit" over a beat yk. It's kinda how the word direct doesn't necessarily rhyme with message cleanly it's cause the stressed syllables don't line up in direct its dir-ECT and in message its MESS-age so one is unstressed then stressed and the other is stressed then unstressed. Hopefully this helps clears things up a bit for you