THEORIES, oh yeah here they come!
I caught the end of some fishing show with Bob Izumi (I think that's his name). He mentioned that many people don't strike hard enough (this was for some bass show). He demonstrated by letting out line in a field, with someone holding the line wrapped around their hand on the other end. He then did the average hookset, and explained that since monofilament stretches, it loses alot of the strength put into setting the hook. Tips were to keep the rod tip down to the water, so as to have the most direct link to your lure. Having a "belly" in your line, from the tip of the rod to the water, often nullifies(word?) the strike or take from the fish. The other tip, strike HARD!
I've watched a few people "miss" hits, and usually its the lazy strike that loses the fish. The strike should be sharp so as to penetrate the mouth. The other factor which seems to come into play is the angle of the line from the fish's mouth to the rod tip. I feel that some techniques are more effective in different cases. If the hook has not gone right through the lip of the fish, you'll lose it once its up close because most people keep their rod tip high, changing the angle at which the hook is set within the lip.
My other theory is with the type of hook, barbed or barbless. Barbless hooks usually have a slimmer profile for the tip. Barbed hooks, even when crimped, have a larger profile. This requires more force for a barbed hook to penetrate, as opposed to a barbless hook. So if using a barbed hook, filing the barb down with a diamond file without ruining structural integrity of the hook may be worth while