Your title, "Nothing in Life Is Written Unless You Write It Yourself," brought a duality to mind. On the one hand, our souls in consultation with other souls and "god" write our soul contracts that I prefer to call improv scripts. I call them improv scripts because human free will can overwrite almost every aspect of the contracts other than dates (not reasons/causes) of death. https://medium.com/illumination-curated/life-is-school-for-the-soul-9b081dbe8453

and fate (soul contracts) + free will = destiny so yes on two levels we write it ourselves