Before anyone downmods hhm for a 'non-relevant' post, consider this: you're flying into Mountain View (San Jose or SF) for the YCombinator interview the day of. Say your flight gets delayed because of the 'weather' but another airline is flying on schedule to the Bay Area.. you will remember Rule 240 and thank HHM. :)

Too bad I couldn't use Rule 240 to argue my way into a free flight on my way back from Novembers YC interviews.. I can picture the airline agent look all smug and say "but sir, your flight was yesterday". Oops!