The diamondback fatalities where I grew up were mostly boaters from the city. They'd pull up on shore, wander off naively through shoreline grass in swimsuits, get bitten, then panic and run. Worst thing you can do; it spreads the venom fast. But if a local happened to get bitten, a very rare occurrence, they'd calmly walk down to the water, keep the bitten limb cool, and send someone for help. Of course, that might be hours away, either pre cellphones or outside of coverage area even today.
My nephew was with a couple of his high school pals way down a remote side canyon on one of the Indian Reservations, when one of them decided to show off and prove he could pick up a rattler faster than it could bite him. I don't need to actually state who won that speed contest. But the creek was right there, so they had him keep his arm in the water. Meanwhile, my nephew walked the five miles or so uphill back to the car, and then drove an hour to the nearest phone. The overall rescue took around 8 hours, and meanwhile, that kid's hand became as big as a baseball glove. He spent two weeks in the hospital; but at least his hand and arm were saved, and he made a full recovery, no doubt quite humbled by the foolish experience.