I wish I had a clever Dave Trott analogy taken from classical mythology, philosophy or a scientific anecdote to introduce this, but I don't.
So if you're aware of an allegory illustrating that for something to work it needs all relevant disciplines on it from the beginning, insert it here.
Basically, if I had a pound for the number of times I've heard stakeholders say, "we're working on the wireframe/customer journey/design - copywriters/content don't need to be involved yet", I would be writing this from my own private Polynesian island surrounded by man servants.
I can't stress this enough, this approach is WRONG!
The minute a UXer is briefed, the minute it's given to a designer, you need to get a copywriter involved.
UX map out the journey, think of all possibilities, test their hypothesis and optimise the customer experience in terms of steps taken to complete an action.
UI (design) will make the web pages intuitive to use, make sure it's optimised for responsive and mobile and that brand assets are correctly used.
A copywriter will make sure the right thing is said at the right time and in the right way. Something the other two disciplines may not think about.
To bring a copywriter in at the end; once the journey has been mapped out, the design signed off and the pages built, means they have no say on where the copy should sit.
And they won't have the background info around what happens next, how did they get there, the requirements to complete actions and what happens if it goes wrong.
I've tried logging into and registering for many a website. It's painfully obvious a copywriter's hand hasn't touched the page. The copy is unclear or it's missing vital information that could've saved a lot of time and annoyance.
A copywriter would identify knowledge gaps that could be filled by handy articles to reassure people moving through or completing a journey.
In this digital-first, fast-moving, highly-competitive, customer-savvy landscape, customer experience reigns supreme. And in customer experience, content is king.
Include your copywriters at discovery phases and enjoy the spoils of increased conversion, traffic and NPS.
Ignore them and it'll be off with your head!