为什么[西方]认为13不吉利

This is going to be a very trying year for people with Triskaidekaphobia, also known as the fear of the number 13.
对于那些患有数字13恐惧症的人们来说，今年可真是难熬的一年。

While the superstitious folks afflicted with this problem can easily stay home on Friday the 13th, it’s going to be a lot harder to stay inside for another 362 days。
以往迷信的人可以在家躲过每个13号的周五，但剩下362天难道也在家宅过去吗？

Why is 13 considered unlucky, anyway?
那么为什么13会被认为是不吉利的数字呢？

There were 13 people at the Last Supper。
最后的晚餐有13个人

It's said that Judas Iscariot and the one who betrayed Jesus - was the 13th man to take his place at the table。
据说背叛耶稣的信徒犹大就坐在饭桌的第十三个位子上。

Similarly, there’s a Norse legend that has 12 gods sitting down to a banquet when the 13th (uninvited) god, Loki, shows up。
同样，在北欧神话中有12个神的宴会，结果第十三个到来的就是不请自来的洛基(最会惹麻烦的神)。

Loki killed one of the other gods, which led to events that eventually resulted in Ragnarok - the death of a bunch of gods, a slew of natural disasters, and the eradication of everything on earth save for two human survivors. There's a lot more to the story than that, but you get the general idea。
洛基杀了其中一个神引发了一系列事件，最终导致世界毁灭：众神的死亡、自然灾害和地球上一切的消亡(仅幸存2名人类)。这个故事远没有这么简单，但你能差不多明白个大概。

Traditionally, there used to be 13 steps leading up the gallows。
传统中通往绞刑台有13个阶梯。

There's also a legend that a hangman's noose traditionally contained 13 turns, but it's actually more like eight。
还有传说称刽子手的纹索上有13个曲纹，但实际上似乎是8个。