Don't you think that Monday the 13th should be scarier than Friday the 13th? To me it has more logic to it- after all Friday is the start of the weekend while Monday is the start of the week. I find, though, that I have pretty good luck on a Friday the 13th, but then I'm not a Templar knight. (As I've mentioned before, they all died that day or were run off.)
I am thinking of superstitions. Writers are prone to them- just as athletes are. Why? Because no matter how good you are at your craft, how good your agent is, a lot of publishing is sheer timing and luck. Try as you might you cannot see reason or logic in our business. As a commenter on another blog said-"everyone knows if the Marketing Director is wearing a green tie, he'll say no to all... (books editors bring to the table.)"
I think this lack of logic can make you crazy. So, in my opinion, the best way to live this life is to think of yourself as water. It flows around the rock, finds the crevices and cracks and slowly shapes the world around it. More simply put- go with the flow and don't take anything too personal. And, if all else fails, be sure to wear your lucky socks. Cheers~