David Barnett has learned a lot since first launching PopSockets more than a decade ago.  As the tale goes, the former philosophy professor was looking for an easy way to hold his headphones and went on to create one of the most viral phone accessories of all time: PopSockets — a device that adheres to the back of the phone and can be used as a kickstand or a handle.  Barnett sat down with Equity this week to talk about his journey building this company from his garage, why he decided to never take on traditional venture capital funding, and some of the lessons he’s learned while scaling the business.  “I was a philosophy professor, so I had no experience with manufacturing,” he recalled, adding that he also lacked experience in business, tax, accounting, and finance.…