In a recent video interview, the Twitter co-founder reveals the principles, technology, and politics that helped shape the now public company.

In the past seven years, Jack Dorsey, co-founder of Twitter and Square, went from two-time college dropout to successful tech entrepreneur. Twitter’s IPO today marks another milestone for Dorsey, who’s one of the youngest billionaires in the country.

During an interview with PandoDaily, the St. Louis native spoke about how Twitter and Square, the mobile credit card payment system, were initially thought to be impossible start-ups: “We were being told ‘no’ constantly with both Twitter and Square,” Dorsey says. “With Twitter, it was ‘Why should this exist in the world?’ and with Square it was, ‘This can’t exist in the world.'”

He proved critics wrong on both accounts. Along the way, he says three main things inspired his work at Twitter. Check out the full video, and our highlights below.

The Promise of Text Messages

As a kid, Dorsey taught himself how to code and program. He got into building maps of cities–using data from police scanners to insert the real-time location of ambulances, fires trucks, and cop cars moving along the urban streets. “I could see the city, I could see it live and breathe,” he says. “I was missing one key element, I was missing the people.”

In 2001 he built a program for his BlackBerry RIM 850 pager, which sent his emails to friends, but it didn’t take off. “No one cared,” he says. But in 2006, he realized his true love, and the missing aspect of his crude maps: “SMS was this rough-around-the-edges technology. I fell in love with it, I thought it was beautiful,” he says. So he brought up the idea of using SMS to share what he was doing in real time.

140 Characters

The idea behind Twitter’s 140-character limit was so that anyone could use it. The cheapest cell phones, which cost $5, can only support 160 characters at a time. He knew he wanted to connect the world–to complete his map–so he settled on 140. “That meant anyone in the middle of Kenya can have the same conversation that Justin Bieber is having on his iPad,” Dorsey says. “It really levels the playing field.”

Besides, having constraints can be a very good thing: “We believe constraint inspires creativity. The 140 characters allows people to be more of-the-moment, off-the-cuff, less shy, less composed,” he says.

A Political Tool

During the first few weeks of Twitter, Dorsey says he saw the tipping point while he was watching one of President Obama’s speeches on TV. His phone went off and it was a tweet from Senator Claire McCaskill from Missouri saying how proud of Obama she was. “I actually saw her on television and I had this immense connection to our government, to my country,” he says. “A process we don’t really understand, feel disconnected from. Suddenly, the thing I was watching on television, with someone on the podium, became very real and very human to me.”