The Japanese people of the past and for the most part of today are still extremely superstitious people and those of the warrior class were no exception. This superstition held the number seven as their lucky number. So a day like today would be considered auspicious.
What is luck? From a modern day standpoint sans superstitions, luck is the thing that is created at the pinnacle of one's efforts or as Seneca quipped, "Luck is what happens when preparation meets opportunity." At times, success almost seems ephemeral so many attribute it to some outside influence and thus, like the Japanese, believe it to be out of their control which is understandable. However, rarely does the person with the least amount of concern or preparation come out victorious. It is usually the person who puts the most care and concern into their preparation that comes out the winner. Perhaps their success is the result of the Gods smiling upon them. Who knows.
What we do know is that anything can happen, but as a martial artist those "anythings" that can happen are decreased with diligent and careful preparation. One of my favorite quotes from Scientific American magazine is, "You fail to the level of your preparation." The culmination of one's preparation finds its way to opportunity and either contributes to one's success or failure and that is why Seneca's admonishment about luck is so apropos for martial artists.
I hope 7-7 is your lucky day! If not, maybe you need a little bit more training. See you in the dojo.