when you throw your right hand the right way, that is with a weight transfer from leg to leg, your head will naturally preform a slipping motion as your upper body moves over your front leg thus concentrating your body weight over your front leg. thats why when two guys are trading a pair of right hands, the guy throwing his right hand the right way, that is with a weight transfer from leg to leg, can slip right hands through the space next to his right ear and over his right shoulder, and the guy who cant, gets hit.
thats cause your right hand is a slip and a punch all in one.
and thats why you can create counters with your jab and use your right hand to simultaneously slip and counter the counter your jab just created.
and that is the main idea of using your jab to set up your right hand.
there is one exception. when you throw your jab and you get a guy to slip your jab inside and throw his counter right hand in the same motion, you cant counter his counter right hand with your own counter right hand. thats because by the time you are just starting your right hand, his right hand was already on its way, coming over the top of your jab. so you turn into it before you can get a chance to slip it through the space next to your right ear and over your right shoulder.
when you throw your jab and you are creating an inside slip a lot, your urge will be to drop a right hand into the path of his slipping motion, right? but the other guy, in knowing this, can throw his counter right hand in the same motion, making you run into his counter right hand as you turn to throw your own right hand.
what i have been driving at, or trying to at least, is that in boxing you must try to think a few steps ahead all the time. that starts with your jab and then you go from there. but the other guy is also trying to think a few steps ahead. what you are trying to set him up with, he may be trying to set you up with, and so on.
try to remember that the next time you use your jab to set up your right hand.