Well it depends what discussions you're getting yourself into.. when they are opinion based such as "should we ban the burka" there is no level ground to come to.. It's a matter of opinion so back and forth is expected, when it's factual for example The Disappearance of Madeline McCann and someone can provide actual evidence (not an opinion) to suggest a point, then you have to take that on board to your opinions, and sometimes it can cause them to change (in my experience)
I agree though, dogmatic assertion makes me stick to my tracks especially when the reason the other person is acting like that is because they simply feel they have more of a say over the matter.
A wise man knows that he knows nothing. Therefor, anyone who is overly confident is an idiot.