> $160k / 2724 pages = $58.73 in revenue pr. page.

It likely ends up being a lot higher revenue depending on the author's life style.

Books and courses potentially have a lot of "back-end" value from opportunities that come up through folks finding you through your book / course.

Here's a couple of excerpts from writing blog posts and making a few video courses over the last 5-6 years:

Wrote a blog post about Flask that took me 3 hours to write but it resulted in 40 hours of contract work from someone finding me through that post. You could say the post directly made $0, but indirectly made a lot more than $0. Stuff like this might happen 8 months after you write the post.

In another case, I made a course about Flask and someone reached me out to me for contract work which resulted in a multi-year long gig which then turned into a full time position and along the way met some great people.

I've flown across the US a few times for tech events (all expenses paid) because of a blog post and got to experience things I wouldn't have gotten to experience on my own.

There's dozens of other events and contract gigs over the years that happened from writing blog posts and video courses. They all resulted in either indirect monetary gains or fun life experiences. A lot of the posts resulted in nothing too but that's ok. To me writing is the reward, everything else is secondary.

I think it can be difficult to calculate the actual added value on this basis or at least, I've found it hard to do so for my own blogging which has also led to substantial paid work.

That's because, although I can trace specific projects and therefore specific revenue to things I've written, I don't know what the counterfactual would have been. Would I have ended up doing another, similar, project instead? How much of a premium can I charge because of the channel through which the work came in?

> I don't know what the counterfactual would have been

I don't think anyone can answer that.

If you take this line of thought to completion then nothing is quantifiable because there's too many ways for events to have an unpredictable outcome when measured over time. For example, you could start walking outside on a windy day, wave at your neighbor without stopping, eventually reach train tracks, pause for 2 minutes to wait for the train to pass, continue walking and then get hit in the face by a $20 bill that happened to get lifted up by a wind gust. If you talked for 5 minutes with your neighbor instead of just waving you wouldn't have picked up $20 because the $20 would have blown away by the time you got there.

Since your life is a series of non-editable events there's no way to know what would have happened in both scenarios. Or to relate it back to this example, writing blog posts, books or courses. The only thing you can do is make decisions that you think will be beneficial for you based on whatever criteria you feel is important. I can say at least in my case, writing these posts and making those courses produced a beneficial outcome and tons of other folks have said similar things about writing.

One thing I've learned is you can't discount great things from happening when doing things that feel minor. It's like the butterfly effect. Someone reading 1 sentence in a blog post you wrote 2 years ago could result in you getting a personal tour from the senior astronomer at SETI's headquarters[0]. Completely unpredictable.

[0]: https://nickjanetakis.com/blog/coming-back-to-cloud-field-da...

The thing that is often missed with opportunity cost is whether more work feasible. Most of us are salaried. Most of us have contracts/policies that say working for another company has to be approved. Even if you find another job, will they actually pay that much and will the hours be flexible enough to rival writing? It's not really lost opportunity cost if the opportunity doesn't exist.

Do most employer policies really require explicit approval for moonlighting? I'm on job number seven, not counting a 4-5 year stint freelancing full time, and none of them required approval. A couple required notification but several didn't mention moonlighting at all beyond the typical "only do work stuff on work machines."

Depends on where you live. It's pretty common that companies don't want you working for competitors. How they implement that depends. Some have non-competes, while some states don't allow them. My company requires approval for compliance reasons (regulated industry).

That’s 136k over six years though, so ~22k/year in “time”, returning ~27k/year in profit. And for this kind of content one hour per page is certainly overestimating.

The trick is that you cannot simply decide to work an extra hour and a half everyday at your day job to get the extra income. Plus who wants to work 10 hour days for years on end?

Of course, there must be some assumption that you either have the ability to do extra work that generates income at work (could very well be the case for consultants), or you can do contract / consulting work yourself.

Writing a book falls into the category of being your own boss/business - but there are also uncertainties.

The author mentioned that he spent around two months on producing a book, and seeing that he's authored 17 books - that comes out to 34 months over 6 year. But I can't find any information on how much time is being spent during those two months. My estimates were almost two hours / pages or writing a day, and with average of 170 pages a book, that came to 80-90 days of writing, or almost 3 months. So it seems I overestimated.

One issue I see with your example. You say “had the IT guy chosen to work”. This statement assumes OP can just pickup more hours easily. That is not the reality. If it’s a salary based position, OP can’t put in more hours just to earn additional income. If it’s a hourly job, OP all can’t put in more hours. Usually anything outside 40 hours is considered overtime and would need to budgeted and approved by the employer. OP could use his IT skills to find more work at that rate for a different company, but now we are back to the passive income example. TLDR. The math makes sense, but the example falls flat in reality.

> Let's further assume that he spent one hour on each page.

That seems extremely low for finished, post-edit text? I would estimate one work-day per page is more likely?

And he's probably pretty dam good at this, lucky and well connected. Articles like this imply everyone can do this which isn't true.