Why this day exists

A text file can describe a program without being a program you can run.

Go gives you a short path from one readable file to one executable file. More importantly, it checks that path before the new program starts.

When something breaks, you need to know who rejected it: the shell, the Go tool, the compiler, or the running program.

That one distinction turns an error from a dead end into a location.

It also explains why changing source text does not change a program you built earlier.