MSN Messenger has >300 million users. QQ has three times that. Why do you find it so inconceivable that Facebook has 750 million active users?

I don't have time for the Socratic method.

Okay, I'll spell it out for you in capital letters:

NUMBER OF USER ACCOUNTS IS NOT THE SAME THING AS NUMBER OF INDIVIDUAL PERSONS. THE NUMBER OF USER ACCOUNTS IS ALWAYS HIGHER THAN NUMBER OF INDIVIDUALS.

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