How do you self-review while writing? What do you mean by that?

I see it as different phases of development, mindset, and focus. You inherently can't be in multiple at the same time.

1. Problem space and solution exploration - an iterative and at times experimental process to find and weigh solutions
2. Cleanup and self-review - document your findings, decision-making, exclusions, and weighing, verify your solution/changeset makes sense and is complete (to intended scope)
3. Reviews

It makes no sense to be thorough during experimental and iterative exploration. That'd be wasted effort.

After finding a solution, and writing it out, a self-review will make you take a systematic, verifying review mindset.