Like Amazon, Airbnb, and many other startup breakthrough stories, Whatnot traces its origins back to a small rental home. But unlike other founder success stories, one of its creators took a rather radical approach to productivity: total seclusion.  Co-founder Logan Head “locked himself in his room for about four or five weeks to build it,” Whatnot CEO Grant LaFontaine told Fortune’s Allie Garfinkle on a recent episode of the Term Sheet vodcast. “He was coding 16 hours a day, six days a week.” Inspired by their own collectibles habits, LaFontaine and Logan Head launched their livestream shopping app in December…