# What makes a question viral?

Recently the question Is this Tetris puzzle solvable? received an insane amount of upvotes, at least four times more than "ordinary" great questions, which only get 20-25.
I really can't understand how this puzzle got more than 100, while the answer received more than 150!
I agree that it's indeed a nice puzzle (I've upvoted it too), the answer is accurate and well-written too, but I don't consider it the best puzzle ever posted in Puzzling (it's a personal opinion, I know, but I think that many think the same).
As a side note, it also got an enormous total of views in few days, which rarely happens for other posts.
What made it so popular to become the highest upvoted puzzle?

• The question is easy to understand and has a picture, and the answer is short and easy to understand. Many of the better and more interesting questions are a lot longer, and lots of people on the internet have short attention-spans! Jun 6 '15 at 9:36

I think the main thing is getting featured on the "Hot Network Questions" sidebar. The number of people in SE generally dwarfs the number of people who read the Puzzling sub, so a mildly interesting puzzle that is featured on the sidebar will get far more upvotes than the most fascinating puzzle of all time that isn't. I don't remember whether that Tetris puzzle was featured, but purely from the voting I assume it was.

As for how those sidebar posts are chosen, I've no idea, I assume it involves exceeding a ratio of upvotes/age or upvotes/timespan. I remember noticing this puzzle on the sidebar and wondering how it got there, since it's a trivial question that was answered correctly in less than fifteen minutes. I think it's fair to say that the fact that it got a dozen upvotes, several elaborate answers, and lots of discussion was mainly due to it being shown to many thousands more people than the typical Puzzling post.

edit: According to the link Emrakul added below, the basic formula for scoring used to add questions to the SE sidebar is:

(MIN(AnswerCount, 10) * QScore) / 5 + AnswerScore
-------------------------------------------------
MAX(QAgeInHours + 1, 6) ^ 1.4


Unfortunately, this may work well for other subs but it's pretty bad for Puzzling. In other subs, a one-hour-old question with five answers may indicate controversy or interest, but here it usually indicates a question that's either trivial or poorly worded. Conversely, older questions with no answers will never be featured on the sidebar, despite that being exactly what a lot of Puzzling users are most interested in.

• For more information on how Hot Network Questions are ranked, see this Meta.SE question. A short summary: answer quantity is heavily weighted; scores are less relevant but helpful; once six hours have passed, the question begins to fall down the list.
– user20
Jun 5 '15 at 18:16
• Thanks, very interesting. Brings up a few thoughts that I'll add to my answer. Jun 5 '15 at 18:27