Nearly three-fifths of all clothing produced ends up in incinerators or landfills within a year of being made.
Notes:
MKinsey has since changed this to "within years". See https://www.vox.com/the-goods/2020/1/27/21080107/fashion-environment-facts-statistics-impact for more.
Primary Source:
2016 - McKinsey & Company, Style that's sustainable: A new fast-fashion formula (2016)