This week on Know It All, Greg Brown and Mitch Moffat from AsapSCIENCE look at why exactly the 90s are back, and how so many trends seem to be cyclical. Inspired by That 90's Show, the new spinoff of That 70's Show, they look at the early days of fashion trends in the court of Louis the XIV, how trend cycles have been put into hyperdrive in the age of fast-fashion, and why nostalgia has such a hold on our brains.