Thirteen is typically perceived as an unlucky number, but I have long chosen to not fear the number or the date and found fun ‘mythology’ type reasons for doing so:
There are 12 months, the 13th is a fresh year — a kind of rebirth.
There are 13 moons in a calendar year.
There were 12 apostles, Jesus was number 13 — a kind of rebirth.
13 is a prime number, divisible only by itself; hinting at a certain integrity and incorruptibility.
The greek god Zeus was considered to be the 13th god, and was the most powerful one.
…I bet there are others, I am just not familiar with them.