"What the hell is database sharding?" I asked my senior engineer 3 years ago. He said, "I'll explain it tomorrow." That tomorrow never came. So I figured it out myself. Here's the explanation he never gave me: Sharding = splitting your massive database into smaller pieces across multiple servers. Think 1 giant messy filing cabinet that takes forever to search through vs 3 organized smaller ones where you know exactly which one has what you need. The lightbulb moment Instead of cramming 1 million users in ONE database, you split them up: Shard 1: Users A-H (333K users), Shard 2: Users I-P (333K users), Shard 3: Users Q-Z (334K users). Searching through 333K records is way faster than 1M records. Simple math.