That is, where users of a point-and-click interface might interact with a computer superficially, the command-line allows for a fluidity of expression and progression of intent that it's extremely difficult to supplant.
When you realize this, the mistake this comic makes is obvious: the command-line is, for many problem domains, simply a superior method of human-computer interaction. In fact, in many ways, it's the GUI that squanders the immense power we have at our fingertips, as it frequently makes it more difficult to express intent rather than less.
For example, here's a basic task: Find all files in a given directory with spaces in their names, and replace those spaces with underscores.
At a command-line I can think of any number of ways to solve this problem. I'd probably opt for a combination of find, sed, and bash looping.
Now try to do this efficiently in any existing GUI interface that isn't purpose built for this exact operation.
The conversations we enter into on the command-line allow us to iteratively build up solutions to problems, solving them with simple, composable tools. There is simply no GUI equivalent.