It really depends on the subject and my experience. When I am at the track I get about 85% keepers. But when I head down tothe beach for surfing I get about 25% keepers as it is not my normal subject. At the wild animal park I am at about 70% keepers but when setting up the lights and trying portraits I am at bout 5% if that. lol.
Good point there, about knowing what you are shooting.
I believe Robert Capa's quote "if your pictures aren't good enough, you aren't close enough" was not talking about physical proximity to the subject, but about knowing the subject.
As an example, I used to shoot a lot of Motorsport, my parents were involved in racing, and i grew up around it. With the photography,it got to the point I could see spins, crashes and accidents happening before anyone else, I could see it in the attitude of the cars, something wasn't quite right.
I occassionally shoot football too, and it's not a sport I'm interested in, so my pics, while being acceptable, are never going to be prize winners, I just don't have the knowledge to see what's going to happen next.
Guys i see regularly who happen to shoot for agencies like Getty and AP, and who love their footy are incredible, they can see what's happening before it happens, but don't have that sixth sense at the racetrack.