When Amazon S3 first launched on March 14, 2006, founder Werner Vogels said he wanted to "eliminate the worry about storage capacity forever." Once you understand what technical decisions that declaration actually led to, S3's distinctive design principles start to come into focus. S3 is not a file system. There are no hierarchical directories, no inodes, no file locks. All there is, is an infinite space of key-value pairs. This article digs into why this simple model has survived even 20 years later, and why S3 questions show up so frequently on the DVA-C02 exam.