While going through the first chapter of "A First Course in String Theory", I read that String Theory being a unified theory should include the Standard Model and in the low energy realm, String Theory should boil down to the Standard Model. To quote the book, String Theory is said to be a promising candidate for a unified theory. Then why is it not so straightforward to get the low-energy theories (semiclassical or non-relativistic quantum) out of it? In particular the standard model? Can string theory be shown to boil down to classical electrodynamics or quantum mechanics?