To add my own two cents- I agree that an upgrade is worthwhile, and I would (and did) do it. However, don't stress about it too much, because assuming you didn't get a Retina model or an Air, you can upgrade the RAM at any time pretty easily. I would also recommend purchasing it elsewhere (read: Amazon) however, because it's cheaper there. Installing it yourself will also give you a little more confidence and ownership of your machine. Putting some physical work into it can be a very satisfying feeling. You may use it at first and never even think you need it, or maybe just stick to 8 GB, which you can find good deals on as well.
One very important detail that Alex did not mention is that a MacBook Pro will not downclock RAM, meaning that you will need to purchase the RAM that is the correct speed for your computer. This isn't a problem on PCs, but for whatever reason Apple's computers do not compensate. HOWEVER- the RAM he pointed you towards is the correct speed, and a good choice. Just a kind of FYI for future reference.
Other than that, I loved his answer. Great analogy.