Why can’t sha256 be reversed easily?

Question

Can’t the steps be reversed one by one to get back the original?

In: Mathematics

Answer 1

Even simpler explaination: Sha256 gives you a number that’s only 256 (binary) digits long, and can be made from a file a million times as long. 

If you took a book and only wrote down the first letter of each page onto a sticky note, you’d never be able to recover the book. But you could easily check whether or not the letters on the note correspond to a book.