Ten Thousand
Ten Thousand
[Caption above the panel:] I try not to make fun of people for admitting they don't know things. [Caption right below said caption:] Because for each thing "everyone knows" by the time they're adults, every day there are, on average, 10,000 people in the US hearing about it for the first time.
[A list of equations.] Fraction who have heard of it at birth = 0% Fraction who have heard of it by 30 ≈ 100% US birth rate ≈ 4,000,000/year Number hearing about it for the first time ≈ 10,000/day
[Caption above the next panel:] If I make fun of people, I train them not to tell me when they have those moments. And I miss out on the fun.
[Megan is standing. Cueball is walking, with his palm out.] Megan: "Diet Coke and Mentos thing"? What's that? Cueball: Oh man! Come on, we're going to the grocery store. Megan: Why? Cueball: You're one of today's lucky 10,000.

This strip argues that one shouldn't make fun of people for not knowing something that's considered common knowledge. The basic premise of the first panel is that, since people aren't born knowing anything , everyone has to learn everything for the first time, at some point. If everyone eventually learns a given fact, there are an average of 10,000 people, in the US alone, who learn the fact for the first time each day. 
The approximate rate of 10,000 people per day hearing about something for the first time is estimated by the birth rate of 4,000,000 people per year divided by 365 days per year, assuming that the birth rate is constant and that indeed everyone learns or gets the fact (or that those in the US who don't are about equal in number to those in other countries who do). The target age of thirty years is irrelevant in this calculation; the 10,000 number is simply equal to the number of newborns per day, or equivalently, the number of people who reach a given age each day.  (The fact that not everyone lives to be that old, and some die younger, is not considered.)
The second panel points out that (certainly, for someone like Randall), teaching people an interesting fact for the first time is fun .  Mocking someone for their lack of knowledge makes them less likely to reveal that they don't know something, which means you don't get the opportunity to share in the experience as they discover it.  Taking this approach is much more socially effective and generally enjoyable than mocking them for being ignorant. When Cueball learns that Megan doesn't know about the "Diet Coke and Mentos thing", he refers to her as "one of the lucky 10,000" who's experiencing it for the first time that day.
Diet Coke is a popular brand of sugar-free soda. Mentos is a brand of chewable mints. Famously, if you drop Mentos into a bottle of Diet Coke, the soda will erupt quite aggressively , sending a fountain of soda 10 feet or more into the air.  This interaction is widely beloved because it's dramatic and unexpected, while being generally safe, simple, and inexpensive to do (though it does make quite a mess, and should only be done outdoors). This effect appears to only happen with this specific type of soda and this specific mint, and is believed to result from a very particular interaction between the ingredients in the two, the texture of the mints, and the carbonation in the soda.  This was explored, in some details, in a Mythbusters episode .
The Diet Coke and Mentos eruption has also been mentioned in a previous strip 346: Diet Coke+Mentos .
The title text provides another, perhaps more emphatic example of how explaining a fact to a person for the first time is much more entertaining than just expressing annoyance about that missing knowledge. Here is a good video about the Yellowstone supervolcano . Interestingly enough, both events includes some kind (although very different kind) [ citation needed ] of eruption.
Supervolcanos are again mentioned in 1159: Countdown and in 1611: Baking Soda and Vinegar .
This comic also appears in Randall Munroe's book How To , in the introduction of the book, albeit in a modified form.
[Caption above the panel:] I try not to make fun of people for admitting they don't know things. [Caption right below said caption:] Because for each thing "everyone knows" by the time they're adults, every day there are, on average, 10,000 people in the US hearing about it for the first time.
[A list of equations.] Fraction who have heard of it at birth = 0% Fraction who have heard of it by 30 ≈ 100% US birth rate ≈ 4,000,000/year Number hearing about it for the first time ≈ 10,000/day
[Caption above the next panel:] If I make fun of people, I train them not to tell me when they have those moments. And I miss out on the fun.
[Megan is standing. Cueball is walking, with his palm out.] Megan: "Diet Coke and Mentos thing"? What's that? Cueball: Oh man! Come on, we're going to the grocery store. Megan: Why? Cueball: You're one of today's lucky 10,000.
