[kbenson]

It's definitely used in slot machines as a lucky number. Which came first I'm not sure (but I suspect from a sibling comment in the same thread it's based on perceived commonality and primeness historically and became "lucky" in the past because of that).

[II2II]

While I have never heard of someone referring to 7 as a lucky number, 7 is the most common sum of two rolled dice. So I can see how people would regard it as a lucky number. Along the same lines, I assume that someone who mentions 42 as a random number has at least some interest in science fiction.

[dontseethefnord]

You must be living under a rock if you’ve never heard of 7 as a lucky number.

[II2II]

I prefer to calculate with numbers, and don't pay much attention to superstitions around them. I don't gamble, nor much pay attention to conversations about gambling, so I pretty much ignore any mention of lucky numbers when such topics arise (aside from knowing that some people have lucky numbers). If you refer being isolated from a particular aspect of life living under a rock, so be it. Though I will point out that I like wide open space. I'm more of an astronomer than a geologist!

[bawolff]

I have never heard of 7 being lucky until this thread.

I think you overestimate how cultural diverse western countries are when it comes to small things like this.