Somehow I managed to develop a pretty good instinct for when something sounded fishy. As facts and details became easier to check, I became more comfortable doubting what I read or heard. Opinions, and the rationale behind them, were a different story, but gradually it's become easier for me to conclude if someone doesn't necessarily believe what he's saying, or can't explain what he's thinking, and what's infinitely more fascinating, why.
In this context it seems strange to consider me argumentative by nature. I am argumentative, but not combative or quarrelsome. However, it's still surprising to me how often people interpret disagreement as a personal attack. It's probably my style, but I do know that people simply aren't used to being asked to back up why they believe something to be true, or offer a rationale for a value judgment. More often than not, it's interpreted as a challenge, rather than welcomed as an opportunity for some good discussion.
There's no better way to learn than by challenging what you think you know.