Have you ever actually been persuaded/persuaded someone else in an argument?

[muon2]

Both Beet and dead0man make the good point that debaters debate for the audience and themselves as well as for their direct debate opponent. Even in a formal tournament it's the judges who must be swayed by the strength of the argument, not one's opponent.

I would also like to expand on Vosem's comment. The core there is that information can move judgements, unless there is a stronger underlying belief. On subjects where one has a significant edge in knowledge and there is little personal involvement, debate can be very effective. Conversely, I find that it is equally effective to be open to points where someone else has the knowledge edge. It shows that person respect and makes that person more likely to concede your points when knowledge is in your favor.