Sequoyah is an interesting example. He had access to English printing and knew that it encoded the English language, but he didn't know exactly how, since he c

Sequoyah is an interesting example. He had access to English printing and knew that it encoded the English language, but he didn't know exactly how, since he couldn't read or write English. He couldn't read or write any language in any script, so in the process of creating a script for Cherokee, he had to independently invent the concept of the syllabary. The proto-Elamite script might also have been invented by someone who know how others used the Mesopotamian script but wasn't literate in it himself. If you learn to read and write one language you'd want to re-use as much of that knowledge as possible when writing a second language (e.g., using romaji to write Japanese) but there's no loss in creating an entirely new script if you aren't literate in any existing writing system.