Jonathan Wegener is the co-founder of TimeHop, which began as “4Square&7YearsAgo” at the Foursquare hackathon in 2011. He gave a video interview to Major League Hacking co-founder Jonathan Gottfried about his experiences.

“We had this idea about a week before [the hackathon], which was to do a replay of your past, in the style of the ghost of Mario Kart,” explained Wegener, a Columbia University graduate who studied sociology and neuroscience. “You’d be friends with the ghost of yourself.”

A hackathon wasn’t enough time for he and partner Benny Wong to make their full product, but that proved to be a good thing. “We scoped, scoped, scoped it down, basically into a daily email… it was a beautifully simple product,” Wegener continued.

Wegener said users liked the simplicity. “When they started getting this replay of the past, they found it really personal and interesting, and they started getting addicted to their daily emails,” he said. “I don’t know why it’s powerful. I just know that it is.”

One reason could be TimeHop’s role as a digital scrapbook. People use it to reminisce, just as they used to by looking through old Polaroids.

On the technical said, “W could never have predicted all the problems we’d run into,” especially with making it scalable, Wegener explained. “We worked with several different APIs which is itself difficult, because there’s always quirks and things being deprecated and things changing and things breaking.” Perfecting the timestamps was a particular challenge.

Sites such as Facebook and Twitter have been independently making it easier for users to archive their own history, he continued. But it’s important not to interfere with the privacy rights of other people — TimeHop could have let users see their friend’s histories, but chose not to do so.

Beyond just scrapbooking, TimeHop is finding that its customers are doing intended things, Wegener said. One user left a to-do note for herself 12 months in the future. Conversely, some users like to remake their past. “We’ve heard dozens of stories of people saying, ‘I went and did that with those same people because TimeHop told me about it’.”