So, when I get handed a new documentation project to do, it goes like this. There's a period of weeks or months where I read the spec, I write a doc plan, I play around with the software, I scrawl incomprehensible diagrams on graph paper, and I think. A lot.
And during that whole time, I get an chorus from release managers, developers, product managers, etc. of "Have you started writing yet?" It starts as a gentle chorus, and gradually gets more strident.
At some point, the chorus begins to dent my serene self-confidence that I know what I'm doing, and I am gripped by an Unreasonable Dread during which I become convinced that I've forgotten how to actually write documentation and that I probably ought to quit and do something more suited to my talents, like guinea pig herding.
Then I pull myself together, build a playlist of energetic music, and begin cranking out documentation at speed.
I've been through this enough times to recognize that this is exactly how it works, but I wonder if I'll ever get to skip the Unreasonable Dread. At least it was pretty short in duration this time around: I think it lasted less than 24 hours.
The funny thing is that with fiction I'm very much a "just dive in and start writing" kind of writer, but that really doesn't work with technical documentation.