A single question on a whiteboard gave Instagram co-founders Kevin Systrom and Mike Krieger the direction they needed to build a $1 billion startup.

The two entrepreneurs would go on to sell their idea to Facebook just 18 months later in a history-making deal. Technology reporter Sarah Frier takes us inside the Instagram story in her book released this month: No Filter.

Although much of Frier's book is devoted to the infighting and culture differences between Instagram and its parent company, Facebook, the early chapters on how Instagram got started provide valuable lessons for any entrepreneur with an idea.

The most important lesson of all--fill a need, not your ego

One week after Krieger joined Systrom at his first startup, Burbn, Systrom decided to change the product. Burbn, he argued, was an app that appealed to their community in San Francisco, giving them a way to find out where they friends were going and to meet them for a fun time.

Systrom said that though their small group of friends liked the app, most people didn't need it. Even Systrom's early investors--including Twitter founder Jack Dorsey--weren't using it.

Systrom and Krieger went back to the whiteboard at a startup co-working space in San Francisco. Together, the two entrepreneurs brainstormed an answer to the question:

"Does it solve a problem most people have?"

The question served as the tipping point, and as the foundational philosophy that guided Instagram's growth. Any app they created would have to serve a need followed by a plan to serve that need in the simplest possible way.

For example, Krieger and Systrom found that the one killer feature that most of their existing users liked about Burbn was its photo feature. In 2010, new smartphone technology meant that anyone could be an amateur photographer.

The problem was that early smartphones like Systrom's iPhone 3G took terrible photos and were hard to share. "Let's focus on photos and solving these problems," Systrom told Krieger.

The most impactful questions are focused on the customer's needs--not yours.

Fill needs for people working from home

To build on that initial question, what needs are you solving during the coronavirus pandemic?

If you teach yoga, you can't hold in-person classes during the lockdown, but your students still have a need for instruction. Offer virtual classes to keep customers happy and healthy.

If you style hair, you can't meet clients at a salon, but they still have a need--desperate need, actually--to cut or treat their hair. You can provide them with videos or virtual consultation sessions to keep them engaged until the doors reopen.

If you are a leader, what does your team need? They need clear and consistent communication during the shutdowns. They need to have a sense of security, control, and a dose of inspiration from time to time. They may have mental health needs they won't express publicly. A strong leader exudes calm and composure when anxiety is high.

What needs do you solve?

It's a powerful question that worked for Instagram and one you should always be asking.