there is a very simple explanation for this

there are a lot of wrestlers who, for some reason or another, work "stiff" which is where they don't pull their punches, they connect with most of their blows, they don't give a shit about the other guy who they are working with in the ring, bob holly (recently let go after 15 years with the wwf) and the team of bradshaw and faarooq were the peole that you had to wrestle when you'd been a naughty boy and vince wanted to make absolutly clear that you wern't to fuck about

a legalised form of giving you a shoeing if you like, but not as simple as a firing, it was designed to make everyone else backstage aware that you'd fucked up and were being punished for it

in the same way that you get people who can have a ruck and are "hard" and peole who can kick the shit out of you because they've got bendy legs

these are legitimate methods to keep people in line

then yu have accidental injuries inflicted by one guy on another, very famous ones being big show smashed open with a steel chair and knocked sparko, hhh going for a pedegree on kurt and the table collapsing giving kurt a consussion (he still finished the match) owen hart nearly breaking stone cold steve austins neck with a piledriver gone wrong, undertaker throwing mankind off the top of the steel cage and into an announce table (dislocating a shoulder, breaking a few ribs amongst other things) and kurt angle doing a moonsault and breaking bob hollys arm (all easily found by looking on youtube)

these are accepted risks and injuries that happen when thngs go wrong

bret's carrer was ended when bill goldberg kicked him in the head and gave him a concussion, he was medically unfit to wrestle again and has recently recovered from a stroke he had while riding his bike

bill goldberg lacked talent, and vast quantities of it, in the same way that if a telentless footballer ended the carrer of a world renowned footballer beause he's jumped in with a 2 footed challenge, wrestling is a 2 man operation, the guys taking the bumps need to be able to bump properly, and the guys who are administering the bumps, should be able to bump the other guy convincingly but without injuring them

it's a very very complex arrangement of things that is designed to give the viewer the thrill of osmething happening, but the players are always safe at all times ebcause they have the skills to work together well

and possibly not easily explanable over the internet