I understand it's from "Think and Grow Rich", but it's a slightly clumsy way to write the sentence. I don't think adding "back" into the sentence was helpful. back = in return of = from it = the desire

The sentence does not make sense. However, it would make sense if you were to say "... attaining the object at the end of it." meaning "getting the desired thing you had in your mind, after you finish doing something. "at the end of it" means at the end of doing something.

" in back of it " should be replaced with " behind it ".