Re: There are 2^256 private keys out there: how big is that number?
I'm trying to understand it but failed. Why not 2^256? They are hashes right? Like strings. All possible combinations. Where is the mistake? 
He's just nitpicking 
and explained that it's not actually 2 to the power of 256 but only until the highest valid private key to be exact.2^256 = 115,792,089,237,316,195,423,570,985,008,687,907,853,269,984,665,640,564,039,457,584,007,913,129,639,936
isn't equal to 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364140,
in decimal = 115,792,089,237,316,195,423,570,985,008,687,907,852,837,564,279,074,904,382,605,163,141,518,161,494,336
Those aren't hash, 0-F character strings are Hexadecimal (HEX).
Most Hashing algorithms' outputs are just in HEX, that's why it looks the same.