I don't know where you live, LS, but in the various English-speaking places that I have lived "it could not have possibly" has never meant the same as "I don't know how," except among a few arrogant, ignorant folks. These are the sort of people of whom my mother was known to say, "I'd like to buy him at my price and sell him at his."
Guth's "inflation" is over 30 years old now. WMAP has confirmed its predictions. You might read the rest of your Wikipedia link and some of its links to learn more.