Because basically, design (at the beginner's level) is a whole bunch of little tweaks until something looks just right. If you are designing in the same environ

Because basically, design (at the beginner's level) is a whole bunch of little tweaks until something looks just right. If you are designing in the same environment you code in, say by making your tweaks directly to the HTML/CSS, you're just going to get frustrated if your tweaks take any longer than a second or so to make and reload your page That's actually a moderately good analogy - even though I disagree with your conclusion. Approaching design like that is like the developers who approach learning development by writing crap and then randomly tweaking and tweaking and tweaking until it sort of runs and does what they want. Neither is a particularly good approach to learning design or development.