Two things in opposition
First some background on the Law of software envelopment, which is:
Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones which can.
Which has been popularly updated to replace read email with "chat".
People like to talk to other people. People like to get information from other people. People like to hear stories from other people. Etc. etc.
People also like to make money. In the West we do that by being at the top of, or a middleman in a transaction. You buy some French Fries at McDonalds and the cashier gets a cut, the fry cook gets a cut, the corporate heads get a cut, the potato farmer gets a cut, the ketchup maker gets a cut, the napkin maker gets a cut, the delivery truck driver gets a cut, the drive thru window speaker phone maker gets a cut, etc. etc.
One simple transaction, buying some french fries, and lots of people get a fraction of that.
Looking at the above transaction though the lens of the Chat Law above, there's another principle in play, and that is eventually if a person makes money off a real world transaction, they'll eventually try to skip the real world part and just make money by being in the middle of the money transaction itself.
You see the Auto makers do it with their financing divisions, you see Apple doing it by trying to get in on payments, you see Twitter doing it this morning by launching real time commerce.
Make enough money selling a product and you'll transition to selling a service, make enough money on a service and you'll transition to making money off the transaction alone.
Easy enough right?
Here's where the two things above are in opposition. Human's love to talk, but there are a finite number of people they can have relationships with, this is popularly known as: Dunbar's number. Dunbar was a researcher that studied and popularized the idea that humans are built to deal with approximately 150 people.
So ideally, you'll probably deal best with 150 people on your facebook, home and work, and other combined social interactions.
The transaction business above is different though. If you take a big cut of someone's transaction, they'll eventually try to cut you out. You might pay 80 cents for french fries, but do you want to pay 10 cents for the ketchup and 5 cents for the napkin? If charged separately you might skip the ketchup or the napkin. But if the fries cost $1, and the ketchup and napkin come free, you won't think twice about it.
The ketchup and napkin people get paid, which is good for them.
An even better business to be in, is the debit card company that makes a few cents off your card swipe when you bought the fries.
While there are hard costs involved in moving ketchup and napkins around the country, there's not much extra cost involved in processing 10 or 1,000 debit card transactions. So if you make your money by taking a penny or two from the middle of a financial transaction, you want as many transactions as possible to take your pennies from (This should probably be known as Superman III or the Office Space law).
Your factory may only be able to produce so many ketchup packets or napkins a day, but the number of debit transactions a company can process is almost limitless. There may come a point of diminishing returns in selling napkins, but if you make money by being a middleman in a monetary transaction, then you want two things: you want to take a small cut (or even better an invisible cut), so that no one bothers to try to cut you out, and you want to be in the middle of lots and lots of transactions so that your small cut really adds up.
So back to Chat and Dunbar's number. You can deal with 150 people. That's biologically hardwired. People with a financial interest want to be part of way more than 150 transactions though, since they only get a fraction of a cent on each one. Therefore, Facebook, Twitter and others who are big enough to try to make money off of being in the middle of your financial transactions, want you to have way more friends and interactions than 150 people. The more interactions that you have that they can take a cut of, the more they make.
Two things in opposition. You can only do so many transactions but they can make more money, the more transactions you are a part of.
Ok, I know this is just a cheesy commercial advertising hero, but I'm a little obsessed with Captain Citrus at the moment. But I think the Florida Juice Association or whoever contracted this character missed an opportunity to promote orange juice to girls too, so I present to you my contribution to the Captain Citrus family: Citrus Girl!. (Captain Citrus's sister seen sitting next to him at breakfast in the 
