For any given subject, there will be competing theories. Or perhaps, a number of theories, some more competitive than others.
To decide between them is hard, especially in the face of a lack of facts. This will often be the case, and you may often be under time pressure, too. Thankfully, in the absence of facts, a debate will often have opinions.
A successful debate requires both sides to put forth convincing arguments for their own side, and against the others. A debate can be enjoyable, but often the debate is simply a mechanism to make a decision, rather than being purely for enjoying a hearty verbal joust.
To do so, there must be a change in at least one side, to yield to the other, or improve on both to something better than either. This is not possible, if you are not listening well. If you do not argue well, you risk being stuck with a worse option.
"strong opinions, weakly held"
Thought path: listening -> speaking -> speak as though you are right, listen as though you are wrong -> http://collierbrown.com/2010/10/01/speak-as-if-youre-right-listen-as-if-youre-wrong/ -> googling -> http://bobsutton.typepad.com/my_weblog/2007/02/why_specialists.html