I will say in my little knowledge that the odds of guessing someone's private key is 0.0001 which means likely impossible,
Where did you get the 0.0001 from? 0.0001 doesn't mean impossible.
The probability of generating a private key that has been already generated by someone else is very very smaller.
But to say that sha256 has nothing to do with private keys proves that you have zero clue about what you are talking about,
A bitcoin private key is just a random number between 0 and around 2
256 (not exactly 2
256).
For generating a private key, all you need is to generate a random number.
You can use SHA256 or any other function to get a private key from any arbitrary data, but you don't have to do that. As I said, a private key is just a random number.
A total Bitcoin private key is 10^77
This is wrong.
There are nearly 2
256 private keys.