Facebook's founding is legend: In a Harvard dorm, wunderkind Mark Zuckerberg invented a new way to connect with friends...and the rest is history. But for the people who actually molded this great idea into a game-changing $300 billion company, the experience was far more tumultuous and uncertain than we might expect.

Mike Hoefflinger was one of those Facebook insiders. As a computer engineer turned marketing innovator who worked with COO Sheryl Sandberg, Hoefflinger had a front-row seat to the company's growing pains, stumbles, and reinventions. In his new book, BECOMING FACEBOOK: The 10 Challenges That Defined the Company That's Disrupting the World, Hoefflinger tells Facebook's coming-of-age saga from the perspective of a keen observer and key contributor.

Today I'm sharing one of my favorite excerpts from Mike's new book that talks about the 4 core lessons you need to know before building a business:

1. Know whether this is your next thing or your last thing.

In its early years, Facebook attracted acquisition offers from suitors including Viacom, AOL, and Google. The most talked-about was Yahoo's 2006 offer of a reported $1 billion. Why did Mark Zuckerberg, at age 22, turn it down? He had a mission and confidence in his ability to grow Facebook into a thriving public company to achieve it. Rather than snap up the opportunity to be acquired, Zuckerberg charted a 10-year-and-beyond course to make the world more open and connected. Thought Starter: Are you building a feature, a product, or a mission?

2. Add by subtracting.

In September 2008, Facebook launched News Feed, a feature to make it easier for users to see what was going on across their connections. In the decade since, Facebook has been vigilant about monitoring News Feed -- and fine-tuning its all-important algorithm -- to continually increase the perceived quality of this "personal newspaper" for each unique user. With screens connecting everyone to everyone and everything all the time, customers' biggest need is not for more things but for fewer things that matter more. Thought Starter: What part of the world are you making easier for your customers to digest?

3. Know your North Star metric.

To avoid getting overwhelmed by data, Facebook selected a single metric that would be the subject of all their growth attention. For AirBnB, this might be the number of nights booked on the service; for Uber, the number of rides. For Facebook, it would be the number of people who found enough value to use Facebook on a regular basis. Over the years, Facebook would become increasingly sophisticated--and exacting--about monitoring user engagement. Using that metric as their guiding light enabled Facebook to focus on improving the value of their core product--News Feed--to deliver the feeling of connectedness people consistently point to about the service. Thought Starter: What is your North Star Metric?

4. Disrupt yourself before someone else does.

In April 2012, Instagram had 30 million monthly users and $0 in revenue. Yet, the 14-month- old photo-sharing app had caught the attention of the Silicon Valley elite, including Twitter CEO Jack Dorsey. Mark Zuckerberg was watching more closely than most. Seizing on its growth and engagement potential, Zuckerberg struck and acquired Instagram for $1 billion. That lofty investment has paid off. With the successful integration of Instagram, Zuckerberg began a string of self-disruption with a purpose: proving that Facebook was the place to be for the world's best builders while expanding his mission through a multi-app strategy. Thought Starter: How would you disrupt yourself? What are you waiting for?

Whether you're building the next Facebook or not, you can apply the key lessons from their early growth and success to your startup.