It means that zero value time.Time when converted to unix time gives you a negative number corresponding to a date two thousand years ago. With the way go insists on using zero values for expressing optionality this is a rather common mistake. Interacting with anything outside the go ecosystem is done in terms of unix time and this makes it very error-prone. And I've seen this trip people off in real life. And yes, you can argue that this is programmer's fault, but this is exactly what makes it a bad design: it makes people's lives more difficult for no real purpose, just because somebody at Google wanted to feel smart that day.