When you cut metal, either with a lathe, end mill, or drill bit, there's a recommended speed that the cutter's edge moves across the metal. When you're drilling

When you cut metal, either with a lathe, end mill, or drill bit, there's a recommended speed that the cutter's edge moves across the metal. When you're drilling something with a tiny drill bit, the RPM necessary to achieve that speed becomes incredibly fast. Cutting tools are like F1 cars: they work best when you run them at the right speed, and that speed is a lot faster than you're going to be comfortable with!