One thing I think I've learned from leading the Alpha Course is that people learn a lot better (here at least) through discovery than through instruction. If I let people figure things out for themselves instead of telling them the "right" answers, it sticks much more. I think also that there is so much in this culture (and ours, too) that runs contrary to the teaching of the Bible, that if I want to teach, I need to "pick my battles." There are only a few things that I consider important enough that I would directly disagree with someone about even if they weren't asking my opinion. For the rest, I'll hold my tongue until a more opportune moment. "Hmmmm, how interesting."
Besides, I'm not always right anyway (but don't tell Tim).