Had interest in printers, and used one a few times at a shared markerspace. I took a class, and messed around in fusion 360.

Got my own printer, spent months printing upgrades for it. Started to print my own designs to solve problems around my shop. Repairs, tool holders, custom containers, upgrades for other tools like laser cutter attachments.

One day, I decided to make an eBay listing for my designs to sell prints on the side. It took off! Bought 6 more printers and ran them constantly to keep with demand.

Now, I've built supply chains for the most popular products, using mass manufacturing techniques. 3d printing is great for prototyping, and even proving there is demand for a product. Anyone with ambition can bootstrap a business off of a $200 machine running in a closet.