Firstly: That is not a "little pain" That could be a sign of anything as mild as bruising to as serious as a broken rib, a punctured lung or worse.
Secondly: While I understand the heroic ideal of working through the pain, and I've been around enough heroic individuals to know it all too well, it is not something I allow unnecessarily. We are not so desperate at the moment or so low on people that you cannot stop and come in for treatment.