It's never "easy" to make a good film. You can trainwreck it at any stage. If you want to see how a film project that has EVERYTHING going for it fails, read the book "The Devil's Candy"
about the making of "The Bonfire of the Vanities", and you can literally watch as all the little decisions add up to make a supposedly sure-fire hit become a gigantic bomb. (The book is also valuable because it's a rare journalistic look at how a film is make, from greenlight to release).