Or just some guides for some topics, even a few examples of how deliberate practice for X might look like is already much better information to start your own practice than these aloof principles. It's great to know the principles if you're also aware on how to apply them, if there's no path to application it becomes mostly noise...

This is why "self help" books are so rarely helpful. They often lack concrete, actionable steps that you can take and simply provide faux-epiphanies.

I do not doubt this author's words, but they did not provide much "concreteness" here.