So I was reading an ok novel yesterday by a highly regarded author, and in the course of one chapter-long action sequence the good guys control three people by hitting them on the head and "knocking them out." Just like, bam, lie there for a while until we're done with our mission, ok? I put the book down. It was "Lost" soured me on the whole business. In the course of the first season half a dozen people must get "knocked out" and left to lie unconscious for a while. It is portrayed as something that anybody with a club can do, a super convenient way to get your enemies out of the way for a while without killing them. Nobody ever suffers any long-term consequences.
But this is fantasy. Really, getting knocked unconscious by a blow to the head is very serious. It often leads to severe brain injury or death. When a head injury patient comes into the ER, what do they ask? "Did he lose consciousness?" And if the answer is yes, they get ready for a really serious case.
Knocking someone unconcscious is also rather difficult to do -- people can be beaten to death without losing consciousness until the final blow.
I am sick of this trope. It is a lame cliche and an act of gross laziness on the part of the writer. Enough already.