To borrow an insight from Allain’s field of computer science, this is context switching. Basically, working on two projects at the same time doesn’t mean you can dedicate half your time to each project. Instead, you may dedicate 40% of your time to each project. The remaining 20% would be spent on stopping to perform a different task on a different project and trying to get back up to speed on the initial project.
UX writing is based on two simple principles: be respectful and be useful. Everything else stems from them. Being concise means respecting people enough to value their time more than yours. It’s you who has to die over the text, not the user. Being clear means avoiding being twofold, protecting from bad experiences, thus, being useful. Being expressive means being truthful and hiding no flaws. Always focus on helping a user first, don’t show off your eloquence, don’t SEO it, and never use marketing cliches — enough is enough.