It's perhaps worth keeping in mind that Kleon is giving this advice about writing books, and that in context, this isn't "you can do it" pithy advice of the sort that DayDollar's comment is mocking. The quote from David McCullough seems to be at the heart of his point:
"When I began, I thought that the way one should work was to do all the research and then write the book. In time I began to understand that it’s when you start writing that you really find out what you don’t know and need to know."
You do have to do some research; you don't charge into your project with no plan. But not only does trying to make the Most Bestest Completest Plan Ever end up being a form of procrastination (see all those folks who've spent years doing worldbuilding for their great epic fantasy novel but still can't tell you what the protagonist's character arc is, or possibly even who the protagonist is, period), it turns out that once you start actually working on the project you get a much, much better sense of what the plan needs to be. You figure out what to write in that part of your outline that says "subplot about Gail's past starts here". You start figuring out more about what the Thing your [Insert Thing] as a Service startup actually needs to insert and so on.
Exactly. People somehow mis-read this as generic advice perseverance porn or something like that when the original essay is just about starting something like an essay/noel (while feeling underprepared) vs. justifying delays through excessive research
"When I began, I thought that the way one should work was to do all the research and then write the book. In time I began to understand that it’s when you start writing that you really find out what you don’t know and need to know."
You do have to do some research; you don't charge into your project with no plan. But not only does trying to make the Most Bestest Completest Plan Ever end up being a form of procrastination (see all those folks who've spent years doing worldbuilding for their great epic fantasy novel but still can't tell you what the protagonist's character arc is, or possibly even who the protagonist is, period), it turns out that once you start actually working on the project you get a much, much better sense of what the plan needs to be. You figure out what to write in that part of your outline that says "subplot about Gail's past starts here". You start figuring out more about what the Thing your [Insert Thing] as a Service startup actually needs to insert and so on.