Despite often talking about slowing down in reading and self-education, I actually agree with this.

When it comes to learning a tightly defined skill or topic to the point of basic proficiency, like copywriting a sales page with a decent conversion rate, you really can learn it in two weeks of intense practice.

You do a project, run into obstacles, and seek out information and techniques to overcome those obstacles. After two weeks of focusing on it for a few hours a day you will become better than 99.99% of the general population at said skill.

Mastery, of course, and even intermediate proficiency, is a much longer game.