It's subjective, but I think a good metric to use is resistance. Whenever you feel resistance towards at task, that's work. Stuff you know you should do, but don't feel like doing.
A common example are textbook exercises in math or physics books. Most people don't mind passively watching lectures or YouTube videos on these topics, but they'll never do exercises that force them to think and produce something from scratch. They feel like work. Doing them is scary because they expose your weaknesses. It's easy to get the illusion of having understood something from watching lecture when in reality you haven't. But when you talk to actual mathematicians and physicists, they will tell you the single most important thing you must be doing are these exercises.
Writing is another common example. Sitting down and writing a book, or a blog, is scary and feels like work. It exposes gaps in your own understanding and knowledge. People have an inherent resistance to this. They'll start, but then drop it and give up early. There are probably 100x more people who have "prepared and organized" a blog or started and outline of a book than people who have kept up the practice or finished a book.
A common example are textbook exercises in math or physics books. Most people don't mind passively watching lectures or YouTube videos on these topics, but they'll never do exercises that force them to think and produce something from scratch. They feel like work. Doing them is scary because they expose your weaknesses. It's easy to get the illusion of having understood something from watching lecture when in reality you haven't. But when you talk to actual mathematicians and physicists, they will tell you the single most important thing you must be doing are these exercises.
Writing is another common example. Sitting down and writing a book, or a blog, is scary and feels like work. It exposes gaps in your own understanding and knowledge. People have an inherent resistance to this. They'll start, but then drop it and give up early. There are probably 100x more people who have "prepared and organized" a blog or started and outline of a book than people who have kept up the practice or finished a book.