I don't think we can flat out deny that accessibility is a complex issue.
And I would argue that it's not an issue you can solve with a complex and detailed plan. Because the true scope and nuances of accessibility challenges will often become apparent only after you get your hands dirty. Your initial plans, while well-intentioned, will miss crucial aspects that surface during implementation.
When you dive in, you'll gain firsthand experience with the needs of diverse users. You'll understand the different technical constraints. And you'll hit unforeseen barriers. As you progress, you'll develop a deeper understanding of assistive technologies.
And this growing knowledge will continually reshape your perception of the problem. Inevitably, you'll make those rigid pre-defined plans obsolete.
Instead, I favour an iterative process, where each step I take forward gives me hints for the next step on the path ahead. Ultimately, through persistent efforts, I'll get to a tipping point. The expertise and insights you gained so far will form a clearer vision of accessibility requirements and solutions.
It's at this stage that I believe I can come up with a more formal plan, if I need to. Often times, I don't.
I find that uncertainty is catalyst for learning and innovation in accessibility.