content: I'm not a biologist by any means but from what I learned in school all animals live to fulfill two purposes: survive and reproduce.  When it comes to interacting with the unfamiliar (a dude on a surfboard) the shark can take 1 of 3 options: Investigate, fight, or flight.  An apex predator like a white shark isn't going to flee from most scenarios, which leaves the first two options.  If he wanted to make a meal of this guy he certainly could have but something in its brain was telling it that this isn't a typical meal-it doesn't behave like a typical meal, and its senses arent telling the shark it's a typical meal.  I know we humans like to make the analogy that a guy on a surfboard looks like a seal and that's why surfers get attacked.  This is sort of far-fetched.  Have you ever seen a seal swimming?  It looks nothing like a surfer.  They're fast, they jump, they dart left and right and up and down.  I suppose for a moment, when viewed from directly underneath, the outline may resemble something like a seal, but beyond that there aren't many similarities.  Seals have a scent that can be detected by white sharks.  Their movements are familiar to white sharks.  This guy, other than briefly resembling the outline, isn't tripping any of the shark's alarms that "hey, this is totally a seal. Better gobble him up".  Even him paddling away doesn't resemble prey behavior.  Even if it was frantic from our human perspective the shark has no frame of reference to a long skinny thing with two army dangly things propelling it forward.  I'm 99.999% confident the shark was simply curious about the surfer and wanted to simply check him out. As for why people get attacked by white sharks occasionally there's two reasons: one is to investigate.  Sharks dont have fingers and arms.  They can't talk.  They use what they have-their mouths, to receive information when determining whether something is worth the effort of a meal.  This is often why white shark victims lose a limb, the shark takes a bite (albeit a very large one), determines that we're far too lean and boney to consume and moves on.  Unfortunately for us that bite can often be fatal.  The second reason is one you alluded to-the shark could be desperate.  Maybe it's been weeks since its last meal and at this point it needs food, doesnt care what it is.  These are the very rare instances when a human is truly consumed by a white shark.  I haven't seen the statistics in a long time but I know there's only a handful of reported cases of humans being fully consumed by white sharks.  White sharks didn't evolve to consume us and we aren't their natural prey.  There's much meatier stuff swimming in the ocean for Jaws to chomp down on.  If life's gotten so tough for a shark that we suddenly become appetizing the shark likely isn't doing very well. Hope this explains things.  Feel free to respond and I'll try to expand some more on some of the details.