What Books are Highlighted the Most Densely?

by Daniel Doyon

One of the many advantages of ebooks over physical books is that they're much easier to highlight. No more scribbled underlines, illegible marginalia, or dog-eared pages — just a swipe of the finger.

Of course, not all ebooks are worth highlighting the same. You'll only highlight something if it's so interesting or so well-written that you want to see it again. This suggests that the more a book is highlighted, the more interesting or well-written it probably is.

To explore this idea, we combed through our data to identify the most popular ebooks in Readwise — a web app that conveniently resurfaces your highlights from platforms such as Kindle, iBooks, and Instapaper — and analyzed how densely they were highlighted.[1]

Here's what we found:

Top Five Most Densely Highlighted Books

The fifty most popular books are listed at the end of this article, but let's start with the five of those that were highlighted the most.[2]

Table 1: The Top Five Most Densely Highlighted Books in Readwise
Rank Title Author Percent Highlighted
1 Sapiens Yuval Noah Harari 78%
2 The Lean Startup Eric Ries 74%
3 Zero to One Peter Thiel, Blake Masters 72%
4 A Guide to the Good Life William B. Irvine 70%
5 Tools of Titans Timothy Ferriss 66%

The Percent Highlighted column represents the percentage of the book's total text that was highlighted by at least one Readwise user — a proxy for how much of the book's material was theoretically interesting or well-written enough to warrant saving for later.[3]

At first glance, nothing on this list jumps out. I've read all these books and can attest: they're all particularly solid. Upon deeper inspection, however, it is somewhat anomalous that a Timothy Ferriss book was one of the most densely highlighted.

Tim Ferriss and Tools of Titans

First things first, every single one of Tim Ferriss's five bestselling books made it into the top fifty, comfortably securing his position as the most popular author on Readwise. (The next most popular authors were Ryan Holiday with three books and Cal Newport and Steven Pressfield with two.)

The interesting thing about Tim Ferriss, however, is that despite his popularity, his books are rather sparsely highlighted — only 33% was highlighted on average whereas the median of the top fifty was 51%. Excluding Tools of Titans, the clear outlier, Tim's number drops even further to 24%.

Table 2: The Books by Timothy Ferriss
Rank Title Author Percent Highlighted
5 Tools of Titans Timothy Ferriss 66%
41 The 4-Hour Workweek Timothy Ferriss 37%
43 Tribe of Mentors Timothy Ferriss 32%
47 The 4-Hour Body Timothy Ferriss 19%
48 The 4-Hour Chef Timothy Ferriss 8%

The puzzle then is: What made Tools of Titans so exceptionally highlight-worthy compared to, say, The 4-Hour Workweek?

Zen and the Art of Nonfiction

Our final observation is that only three of the top fifty books are fiction; the rest are nonfiction. This is unsurprising, of course, as fiction is generally read for entertainment whereas nonfiction is generally read for wisdom. In other words, you'll probably casually read Harry Potter rather than vigorously taking notes (unless you aspire to be the next big young adult author or something).

Accordingly, you'd expect much less highlighting of fiction than nonfiction this is clear in the stats. As mentioned above, the median of the entire top fifty was 51% whereas Ready Player One and The Martian were highlighted only 5% and 4%, respectively — by far the lowest percent highlighted in the top fifty.

That being said, Zen and the Art of Motorcycle Maintenance — the third and final work of fiction to make it into the top fifty — shattered this norm with a staggering 37% of its text highlighted.[4]

Table 3: The Most Popular Fiction Books in Readwise
Rank Title Author Percent Highlighted
42 Zen and the Art of Motorcycle Maintenance Robert M. Pirsig 37%
49 Ready Player One Ernest Cline 5%
50 The Martian Andy Weir 4%

Perhaps this means that Zen is more profound than your standard work of fiction? Obviously. The more practical takeaway is that Zen and the Art of Motorcycle Maintenance should probably be considered less a fictional, semi-autobiographical novel, and more a nonfictional, philosophical inquiry. It's filled with pearls such as this excerpt (resurfaced from my own collection):

"You look at where you're going and where you are and it never makes sense, but then you look back at where you've been and a pattern seems to emerge. And if you project forward from that pattern, then sometimes you can come up with something..."

Top Fifty Most Highlighted Books

Without further ado, here are the fifty most popular books in Readwise, ranked by Percent Highlighted:

Table 4: The Fifty Most Popular Books in Readwise
Rank Title Author Percent Highlighted
1 Sapiens Yuval Noah Harari 78%
2 The Lean Startup Eric Ries 74%
3 Zero to One Peter Thiel, Blake Masters 72%
4 A Guide to the Good Life William B. Irvine 70%
5 Tools of Titans Timothy Ferriss 66%
6 The Obstacle Is the Way Ryan Holiday 66%
7 Thinking, Fast and Slow Daniel Kahneman 66%
8 The Inevitable Kevin Kelly 65%
9 Deep Work Cal Newport 65%
10 The Checklist Manifesto Atul Gawande 61%
11 The Subtle Art of Not Giving a F*ck Mark Manson 60%
12 Choose Yourself! James Altucher 59%
13 Love Yourself Like Your Life Depends on It Kamal Ravikant 59%
14 The Hard Thing About Hard Things Ben Horowitz 59%
15 Rework Jason Fried and David Heinemeier Hansson 58%
16 Steal Like an Artist Austin Kleon 58%
17 The Everything Store Brad Stone 57%
18 Man's Search for Meaning Viktor E. Frankl 56%
19 The War of Art Steven Pressfield 55%
20 Manage Your Day-To-Day Jocelyn K. Glei, 99U 55%
21 Influence Robert B. Cialdini PhD 54%
22 How to Fail at Almost Everything and Still Win Big Scott Adams 54%
23 Antifragile Nassim Nicholas Taleb 54%
24 The ONE Thing Gary Keller, Jay Papasan 52%
25 The Art of Learning Josh Waitzkin 52%
26 Meditations Marcus Aurelius 51%
27 Essentialism Greg McKeown 51%
28 Ego Is the Enemy Ryan Holiday 49%
29 The Power of Habit Charles Duhigg 47%
30 Mindset Carol S. Dweck 47%
31 Creativity, Inc. Ed Catmull and Amy Wallace 46%
32 How to Win Friends and Influence People Dale Carnegie 44%
33 Quiet Susan Cain 44%
34 The 7 Habits of Highly Effective People Stephen R. Covey 43%
35 Steve Jobs Walter Isaacson 42%
36 The Life-Changing Magic of Tidying Up Marie Kondo 41%
37 So Good They Can't Ignore You Cal Newport 41%
38 Anything You Want Derek Sivers 40%
39 Elon Musk Ashlee Vance 39%
40 Do the Work Steven Pressfield 39%
41 The 4-Hour Workweek, Expanded and Updated Timothy Ferriss 37%
42 Zen and the Art of Motorcycle Maintenance Robert M. Pirsig 37%
43 Tribe of Mentors Timothy Ferriss 32%
44 Shoe Dog Phil Knight 26%
45 Principles Ray Dalio 25%
46 The Flinch Julien Smith 20%
47 The 4-Hour Body Timothy Ferriss 19%
48 The 4-Hour Chef Timothy Ferriss 8%
49 Ready Player One Ernest Cline 5%
50 The Martian Andy Weir 4%

Comments and Questions

Feel free to tweet any comments or questions at @readwiseio or email us at hello@readwise.io.

Also, if you happen to read and highlight ebooks, sign up for Readwise and start conveniently revisiting the best parts of what you've read today.

  1. Thanks to Readwise user Florent Crivello for inspiring this article with a tweet. ↩︎

  2. Regarding methodology, the fifty "most popular" books refers to the books that appeared most frequently in our users' libraries (implying at least one highlight) without regard to how intensely those books were highlighted. ↩︎

  3. We experimented with a variety of other metrics such as the median number of highlights taken by each user for each book, the median number of highlights for each book divided by book length, and so on, but we opted for Percent Highlighted because it seemed the most robust. ↩︎

  4. As another point of reference, the next most popular work of fiction in Readwise is Seveneves, which was only highlighted 5%. ↩︎