There are lots of good points made here, but I'll add one: write the environment in itself. The original vision for Smalltalk is that you would be using some application, get curious about how it worked (or want to change it), press ctrl-C to start a debugger, start reading code, start editing, get curious about how the debugger works, press ctrl-C again, start reading code, start editing... That smooth progression from application user to programmer to tool developer was a conscious design goal of Smalltalk (also of Lisp), and has gotten lost somewhere along the way. Once you take responsibility for your own tools you quickly learn to use your new-found powers sparingly, but it's a completely different feeling being a programmer in an environment you can modify than being a programmer in an environment someone else made and you can't touch.