In the most recept episode: we discover that if the plane had never crashed....Jack has a teenage son & Hurley is the luckiest man alive.
In the alternate reality, where the plane does crash, Jack is childless & Hurley has terrible luck.
Theory: Jacob caused misfortunes for both of them to eventually lead them to the island. In the case of Jack, he was the 'other man' his wife was involved with.
Proof that Jacob is evil: In season 2 or maybe 3, Carl is being punished. He is strapped to a chair & is exposed to extremely loud music with crazy images on a screen. One of the images says: God loves you like he did Jacob. Is Jacob really Lucifer?