I remember watching Dragonball-Z, where Gohan’s mom, Chi-Chi, wanted him always to get a PhD. This really hammered home of getting the importance of the credential, the PhD, to be recognized as an expert. However, since that time I’ve become somewhat of an autodidact that learns just for the sake of. However, I recently tweeted this:
You can "get" a PhD in eighty books. 5 books per semester, 4 years undergrad and 4 years grad. 2 * 5 * (4 + 4) = 80.— Dillon Chen (@dillchen) November 1, 2017
The response was surprising. However, I stand by the statement. I first stumbled across this quote while reading "The Mathematical Experience.” The "80 book benchmark" shattered the final remnants of the childhood illusion that you need a PhD to become an expert, a PhD being some mystic level of achievement. In its place now stands a new belief, that becoming expert-level is not that hard. It’s a concrete milestone that anyone sufficiently motivated can achieve.
I really like this 80 book expert benchmark because it has all the classic signs of a good goal. It’s measurable, achievable, but still decently ambitious, especially if you love books. Becoming an “expert” is not that hard, especially if you don’t need the credentials. And thankfully, if you work in startups or are creating something, credentials are not that important. If you really do need credentials, you can always hire someone with the right three letter acronym.
80 books, while seemingly daunting is not that bad. An average US working citizen spends almost an hour commuting to and from work. If she decided to use that time instead of ‘gramming or texting and instead read, she’d be able to get through a decent amount of a book per year. For a book printed with normally-sized font, a reader of this blog could probably read a page per minute. This includes the appropriate highlights made in-text for subject matter retention. That means you, dear reader, could probably finish an average-sized book per week, ~360 pages or ~50 books per year. You could get a PhD in 2 years with time to space! 
The eighty book-mark is also great because it illustrates how little knowledge an individual needs to know to become an expert. Within startups specifically, the low barrier to becoming an expert makes investment decisions in “inexperienced” or “young” founders less risky than they actually are. I’ve already written on how young founders often found the biggest, baddest, and best companies. If you believe the thesis of this piece, then being young is less of a disadvantage because it’s so easy to get up to speed in an industry.
Expert-level specialization is very real and necessary. Even a small town library will usually have at least a few thousand books waiting to be checked out. If we only know 80 books worth of knowledge, it’s hard to imagine how you’d be able to build a multi-faceted business. Also with knowledge expanding at an exponential rate, it seems even more daunting. This is one of the reasons why being an expert or getting things done in the world still requires you to collaborate with others and/or use tools to manage knowledge.
Of course, the 80 book goal doesn't cover all the nuances of being an expert. On Twitter, others brought up several counterpoints. First, books aren’t always the best source of knowledge. I think this is certainly true. To the original goal, I would then add the caveat that, you do need to read 16000 pages—or 80 books worth of material at 200 pages per book. This is especially true in fast-growing fields such as blockchain or AI, where preprint, blogs, and Twitter. Where you choose to get the 16k pages certainly makes a difference in what you learn. The best practitioners are often the ones that aren’t teaching the subject. Their knowledge is either much more implicit, or codified in a much more free-flowing form factor such as a blog post. Take, for example, some of Vitalik’s writings on cryptocurrencies. If you’re getting into crypto, his posts will serve you much better than any book proclaiming that blockchains are the second coming of the internet.
Another common retort to “80 books" was that being an expert is mostly about creation. However, I’d say people still need some base level of knowledge to be able to be productive in a field, and as we’ve established before 80 book-length pieces of information or 16,000 pages or two years of learning seems about right to me. You’re probably familiar with the “Whartonite Seeks Code Monkey" or “I can handle the business side" meme pages. In short, they both poke fun at B-School students who don’t really understand the mechanics of product or startups. When I first read TechCrunch and watched the Social Network, I 100% asked a technical friend of mine the same questions. I didn’t have the requisite mental models on what a “startup” was to know why this was a bit silly of a request. Yet after reading blogs, working on products, and talking to folks to get the implicit domain knowledge, I now do. More generally, understanding the domains lets you know what's at the "adjacent possible", the stuff that's hard enough that no one's done it yet and not impossible. In physics this would be the difference between working on gravitational waves and working on time travel.
I look forward to getting my PhDs in bio, brains, and blockchains soon :)
 The speed at which a person reads will definitely depend on the subject matter as well. While reading Molecular Biology of the Cell, I read at approximately 15 pages per hour while taking detailed notes. At 1000+ pages, MBOC would take me ~70 hours to read it cover to cover. A normal college-level bio class probably covers half the material in the book. So I could a semester in ~40, or a normal work week. Of course, the caveat to this is that I can read 8 hours per day… Of course, I don’t, but for sufficiently motivated individuals who find the subject matter at hand interesting, you could do it. Warren does it.