Hi Thomas,
There have been a lot of interesting points and fascinating sidebars raised in this thread. I generally prefer to contextualize my statements as much as it's practical to do so and I find value in others doing so as well.
At work in particular, I take a very data-driven view on technical issues, so when someone says, "Such-and-such ALWAYS happens," or "X is NEVER an issue," my valuation of their opinion immediately drops a few points. If they say, "I don't recall seeing that issue," or, "In my experience such-and-such is very common," then I may not know a lot more about the topic under discussion, but I do know a lot more about their ability to contextualize their own experience. Of course, better yet is, "We examined 1000 instances of XYZ and found that such-and-such happened conclusively 900 times with another 50 occurrences showing a high probability of such-and-such as well." That's something I feel comfortable acting upon.
I drive my wife crazy with this kind of stuff at times, "Do you know that to be true or do you believe it to be true?" Oh boy, makes her want to kill me.
_john