Internal state of sha256 is 512 bits, though the inputs the user can control are limited to about 300 bits. In any case, it's larger than the believed number of

Internal state of sha256 is 512 bits, though the inputs the user can control are limited to about 300 bits. In any case, it's larger than the believed number of atoms in the observable universe. The important point is that there is no progress, each attempt has an independent probability of success. Imagining it as an infinite haystack with a difficulty controlled density of needles still yields the right understanding.