#Bitcoin  pill n.2:

A private key is an integer number.

A private key more precisely is an integer number which ranges (in the hexadecimal system) between 1 and FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141

There are then approximately 10^77 possible private keys usable in the Bitcoin network.

It is estimated that there are between 10^78 to 10^82 atoms in the known, observable universe.

Therefore trying to find a specific private key is almost like trying to find a specific atom in the observable universe