“Knowledge makes a man unfit to be a slave.” — Frederick Douglass

When Elon Musk was asked how he built SpaceX, the space exploration startup that aims to make humanity a multi-planetary species, his answer is two-fold: reading a lot of books and talking to a lot of people.

“Once he has a goal, his next step is to learn as much about the topic at hand as possible from as many sources as possible,” revealed Jim Cantrell on Quora, who worked with Musk on the founding team. “He literally sucks the knowledge and experience out of people that he is around.”

It’s an approach that has been tried and tested by some of the most successful innovators in history. When working on human flight, the Wright Brothers read on aerodynamics at the Dayton library. Similarly, when Musk explored how to enter the space industry, he increased his existing pool of knowledge by searching for the most difficult books and the world’s leading experts in the industry. He entered the industry as an outsider with little knowledge, and was able to do with $1 billion what NASA was unable to with $27 billion.

From a young age, J.K. Rowling understood that a voracious reading habit was vital to become a great writer. In an interview with literary magazine Words with Jam she described herself as, “your basic common-or-garden bookworm, complete with freckles and National Health spectacles,” shows how much her life revolved around books. And it paid off. Her appetite for reading helped her imagine and create the world of Harry Potter. Her reading directly influenced her writing, which not only made her the first billionaire author but inspired millions of young kids to enjoy reading books.

To this day, she continues to read. As she continued in the interview, “I read when I’m drying my hair; I read in the bath. I read when I’m sitting in the bathroom. Pretty much anywhere I can do the job one-handed, I read.” According to Rowling if you don’t like to read, you haven’t found the right book.

Bill Gates read so much that his parents had to make a rule that no books were allowed at the dinner table. Great books make you smarter and expand your worldview, enabling you to grow to uncharted heights as a result. Reading a book is the original virtual reality. Whatever knowledge you obtain is yours to keep. If you want to store the entire history of the human spirit in a single house, as Hermann Hesse wrote, you can only do so through the collection of books.

Reading books — or anything, for that matter — is a fantastic vessel to explore your curiosity. These days with the internet, reading what has caught your interest can be as adventurous as if you were a detective solving a case. The plethora of footnotes and related content can keep you engaged for hours. Just make sure you consider the quality of the source.

Some of the oldest books are as applicable today as they were one thousand years ago. Take the Declaration of Independence, the foundation of the United States. It was crafted so carefully and thoughtfully that since its inception, it has been amended only twenty-seven times. Most new books are just old ideas that are repackaged and customized for the context of a new generation. It’s likely that in books, your problem has already been discussed and a possible solution is attached. During his time at the military college, Napoleon, who was teased by his fellow students, turned his loneliness into a reading habit. His favorite book was Plutarch’s The Lives of the Noble Grecians and Romans. As they say, the best books have many old books inside them.

Reading books can make you feel as if you are taking a trip, regardless of where you are, by forcing you to challenge your current thinking and imagine the impossible. They also increase your ability for conceptual thinking.

However, it is not enough simply to read. Reading, in many ways, is like eating. If you only eat junk food, sooner than later the consequences will show. If you want to understand anything meaningful, you have to tackle something difficult. Granted, it’s daunting to read difficult material. It’s challenging and it feels like work at first. But like all things worthwhile, if it were easy, everyone would be doing it. It is not enough to read and it is not enough to read seemingly high-quality books. You need to read in a critical, skeptical, and alert fashion.

During my time as an undergraduate student at the London School of Economics, my professors assigned me entire books or chapters from several books every week… for a single class! It was the new normal for my reading diet. I was easily overwhelmed. Over time, however, I learned how to finish it by reading for hours, taking notes, forming connections, and enjoying the exercise. The more I read, the easier it was to handle and appreciate it. By tackling difficult readings, I challenged my thinking and expanded my intellect. Books enable you to explore something deeply in a way that no other media allows you to.

Make sure that you read above your current level of expertise. A book should stimulate our thinking and make us return to consult specific passages. As writer Franz Kafka illustrated, books should wound or stab us — in other words, challenge us. He likened a good book to an ax that we can use for the frozen sea within us.

We also need to read widely. Fiction, in particular, is underestimated as a method for self-improvement. It allows us to shut down to function better when refreshed. We often see fiction as entertainment, yet it shows reality in a way that nonfiction could never do.

Also read the classics, those ancient books that nobody reads. They have withstood the test of time and contain a higher signal-to-noise ratio of value.

While you may be disappointed by now, since reading books is probably nothing that you didn’t already know, it is nonetheless important to value it as an integral part of life. Reading long and difficult texts in a world that caters to our increasingly short attention spans is a road less traveled. So lengthen your attention span, pause your social media and pick up a book.

As Seneca suggested in his Letters, “We should hunt out the helpful pieces of teaching and the spirited and noble-minded sayings which are capable of immediate practical application and learn them so well that words become works.”

When you cannot find answers in books, consult people, as current and special knowledge often resides in private networks. Mentorships are a great way to have enlightening conversations regularly. A good mentor understands your situation and provides you with specific feedback.

Certainly above average, one way that helped Bill Gates get into Harvard was by asking questions. As he revealed in his personal digital journal, “I learned from Mrs. Caffiere that my teachers had so much more knowledge to share. I just needed to ask. Up through high school and beyond, I would often ask my teachers about the books they liked, read those books when I had some free time, and offer my thoughts.”

As former U.S. Secretary Henry Kissinger understood, engaging with people in conversations provides another layer of acquiring knowledge. Conversing with people and asking questions complements reading, too. It offers you a different experience from reading. While reading is solitary, asking questions is a sociable activity.

To tap into the knowledge of private networks, learn how to find the people that have the knowledge that you seek and how to ask questions that will give you that knowledge. Most people are willing to help you find the answer to a question if you ask in a polite and thoughtful manner. We have more access than we think to the people that can move us forward. And with the internet bringing email, and twitter, everyone is more accessible than ever. Even if they don’t reply, you’ve lost nothing from trying.

Another way of investing in knowledge is to learn by doing. As Benjamin Franklin advised, “Tell me, and I forget; teach me, and I may remember; involve me, and I learn.”

Martin Luther King, Jr. was well aware of the rampant racism that was plaguing American society. He recognized the progress that had been made to end racial segregation, but many problems remained. He decided to dedicate his life to solve them. Inspired by Gandhi’s activism, Dr. King organized civil rights protests and risked his life to champion civil rights for African Americans. What distinguished him from others was that he was actually doing something about those problems. He didn’t know how to do it, yet learned by doing. Although he was assassinated, his death became an eternal symbol for the civil rights movement, inspiring others to follow in his footsteps.

During my time at graduate school, I became involved with the innovation lab, a building dedicated to entrepreneurs that allowed them to experiment with their ideas. I always thought that the primary purpose of a university should be to turn thought into action. I loved the intersection of thinking and action, and the lab was the perfect platform to explore my ideas.

The innovation lab was a great way of learning, complementing the reading and study with a practical component. It was certainly challenging to work on your ideas. I’ve experienced many trials and errors along the way, yet these failures taught me something that I could not have learned anywhere else.

As Franklin said, experience is the best teacher. You need to experiment with the knowledge that you acquire — or, as Buckminster Fuller put it, you learn by trial and error, error, error. Beyond different methods of acquiring knowledge, it’s important to emphasize having a foundation. Before you can get into the details, it is crucial to understand the basics upon which all the details build. If you can build a strong foundation of the knowledge that you want to acquire, you will have an easier time building upon that knowledge. In that way, building knowledge is like building a house — it requires a strong foundation.

As we have seen, there are many different ways you can invest in knowledge. From reading, to asking questions and talking with people, to learning by doing — each process has its own unique characteristics. These are only some of the ways that have helped me in my quest to become a better learner. There are countless more that I haven’t mentioned. But beyond finding the perfect methods of acquiring knowledge, the lesson is to find the methods that suit you best.