As an entrepreneur building a company, you should always be focused on learning from those who came before you. With that goal in mind, I’ve documented five lessons from five entrepreneurs who shared their wisdom at Startup School.

Diane Greene

Current: Founder of stealth-mode company and board member at Google
Past: Founder of Vxtreme (acquired by Microsoft) and VMware (NYSE: VMW and acquired by EMC)

Lesson 1: Have a big vision and be persistent.

When you have a big vision, and work diligently toward it, you will attract the right resources. Diane Greene set out to build VMware during the dotcom implosion. It was a difficult time to get funding, but her passion for her idea attracted the brightest minds and the biggest wallets.

She knew recruiting Larry Sonsini to her board would position her company for success. Larry has been a part of nearly every major tech deal in Silicon Valley. The only problem: she didn’t know him. But when you have a big vision and are passionate about it, you will find a way to succeed.

Diane knew an attorney at Larry’s firm and promised VMware’s business, contingent on the attorney setting up a meeting with Larry. Unfortunately, she met with Larry on a Friday afternoon and he said he was not currently interested in joining any new boards. But when you’re passionate about your vision, you see opportunity when others see obstacles. She took the opportunity to talk to Larry about her vision for VMware. She left his office feeling disappointed that he didn’t accept her offer, but content knowing she gave it her best shot.

On Monday morning at 6:00 AM she received a voice mail from Larry Sonsini. He was ready to join her board.

Jack Dorsey

Current: Founder of Square
Past: Co-founder of Twitter (NYSE:TWTR)

Lesson 2: Create a list of dos and don’ts.

Jack Dorsey is known as one of the founders of Twitter and current founder of Square. At the age of 36, two incredibly successful companies is a major accomplishment. So, how does he do it? Jack let us in on his secret weapon: a do list and a don’t list.

Do — Stay present, be vulnerable, drink only red wine and lemon water on the weekdays, do six sets of squats, run three miles, meditate, say hello to everyone, video journal, and get seven hours of sleep.

Don’t — Avoid eye contact, be late, eat sugar or wheat, or drink hard alcohol.

It pays off to create a list of things you want and don’t want in your life if you plan to be a successful entrepreneur.

Chase Adams

Current: Founder of Watsi
Past: Pacific Community Ventures and Peace Corps

Lesson 3: Let go of fear.

Chase Adams had a brilliant idea for a company. While he was working for the Peace Corps, he saw firsthand the power of connecting real stories of people in need to those who could assist them. He worked on his idea for months. When he emailed friends and family to announce his company, he received a lukewarm response.

Unwilling to give up, he started to brainstorm. He wondered where he would find people interested in his project. Then he had a brilliant idea: what if I posted this to Hacker News? His fear set in as he recalled witnessing other entrepreneurs face scrutiny and ridicule after posting their ideas. He decided to post and wait for the outcome. After posting his idea, he received 16,000 visits to his site and 100 percent of his projects were funded.

A few months later, Paul Graham, founder of Y Combinator, read about Chase on Hacker News and sent an email requesting a meeting. An hour after the meeting Paul made an investment.

Chris Dixon

Current: Partner at Andreessen Horowitz
Past: Founder of Hunch (acquired by eBay) and Site Advisors (acquired by McAfee)

Lesson 4: Be willing to take on problems that are not popular.

Sometimes good ideas look like bad ideas. The big companies are already focused on the ideas that look good. It’s up to entrepreneurs to tackle those problems that are not obvious. Some times those not so obvious ideas look like bad ideas.

Many of today’s top companies were initially met with disapproval. Google, eBay, Kickstarter, and AirBNB struggled to find initial traction with investors. Many dismissed them as too niche or structurally flawed. However, the entrepreneurs behind these companies knew they needed to be open to criticism and rejection if they wanted to succeed.

If you are focused on building a billion dollar company, you have to be willing to filter the naysayers. Not all good ideas are obvious at first.

Nathan Blecharczyk

Current: Co-founder and CTO of AirBNB
Past: Stellar engineer

Lesson 5: Don’t quit until you’ve given it 100 percent.

We all know and love AirBNB, but few know that success did not come easy for the company.

Following in the footsteps of Twitter, AirBNB launched at SXSW. The company hoped for astronomical success, yet only yielded 12 sign ups. Undeterred, they heard that the Democratic National Convention was in a few months. They reached out to property owners and signed up 800 properties per week. Their story was picked up by the local news channels and CNN International. Yet again, the results were discouraging.

Believing that they wanted to give it 100 percent before closing shop, they applied to the Y Combinator program. They were accepted, but unfortunately their acceptance was during the most difficult time to raise capital for startups. They were told to get “ramen profitable,” an expression that is used to describe the state of barely breaking even. They worked from 8:00 AM to 12:00 AM every single day to figure out what was needed to make their company a success.

Their big breakthrough came when Paul Graham told them to, “Do things that don’t scale.” They focused on their most devoted market: Manhattan. They flew to New York and met with forty committed renters. They built relationships, offered to take professional photos of the properties, and wrote property descriptions for free.

A few months later, an investor they met through Y Combinator was impressed by their vision and tenacity and wrote them a check.

In summary, entrepreneurs need to be persistent, humble, and focused. You will fail in the beginning. People will laugh at your idea. The idea of quitting will haunt you. You will feel like a complete loser. The biggest lesson I learned at startup school is that winners are resourceful and they find opportunities. They don’t make excuses for why it won’t work. They get focused on ways they can make it work.