Physical Danger
Yeah, the aieee, splat thing.
There's nothing like the threat of imminent, fiery, painful death to make ya focus. But statistically, planes are safer than cars. Most pilots feel vastly safer in the air than they do on a freeway at 11:30PM on a Saturday night surrounded by drunks.
There's another element of the physical here in that pilots have to be in decent physical shape to even be allowed to fly. Eyes must be at minimum performance levels. Blood pressure and weight have to be under control, etc. The situation isn't like a line worker complaining about prejudice against fat people in filing a legal claim against his employer—in this case, if a pilot has a heart attack while in the air, hundreds of people die with him.
The rules are real and the restrictions are serious.
As part of something called the armed pilots program, pilots are even allowed to keep a gun handy in the cockpit, just in case there's any terrorist activity on board. Which means new pilots need to get gun training in addition to simply being shown the ropes at the controls.