[BjoernKW]

The C64's BASIC prompt. The concept of a computer booting into an environment - an empty canvas, if you will - that allows you to immediately create something was ingenious.

Similarly, what sparked my interest in web programming was the ability to view the page source code in order to see how a specific result can be achieved.

While perhaps not going as far as the web's original creators envisioned it to be (the user being able to directly edit and publish from the browser itself) this feature allowed you to quickly learn from and build on existing code as well as try out new patterns and practices.