I took me nineteen years to learn not to argue about facts. I remember realizing it one day while riding in a car, having the usual argument with a person who shall remain nameless but loved to argue, when it occurred to me: why the heck are we arguing about this? Either I'm right, or he's right, or neither of us are right, and we'll find out when we go home and look it up.
Facts - facts that can be known or verified in some manner - are facts. What's the use of arguing about them? Now when I get into a disagreement about a fact, I meta the conversation: "We'll look that up when we can, but let us suppose that it is or isn't true for the moment. How does this affect what we're discussing?"
Of course, everyone basically understands that you can't win an argument about opinions: "This is better" or "That is better". No, "This is better to me", and "That is better to you". Better is in the eye of the beholder.
Even taking that conversation to meta level, you end up arguing "This is better because this has such and such properties, which are more important" vs "That is better because that has these other properties, which are more important". It's still in the realm of opinions.
For instance: Windows vs Unix. I think Unix is better. That's because I value X, Y, and Z about operating systems, which Unix is better at. If someone else values A, B, and C about operating systems, and Windows is better at these, then they think that Windows is better. So the real argument is whether X, Y, and Z are more important qualities in an operating system than A, B, and C.
Which is still a matter of opinion.
I'm sorely tempted to leave the post at this, because the statement:
There are two things you should never argue about: facts and opinions.sounds like it encompasses all things, which would lead to the implied assertion: "You should never argue."
However, there is another thing, other than facts and opinions: ideas.
Ideas are when you argue about what it means that some people believe X, Y, and Z are more or less important than A, B, C in the design of an operating system. We're still arguing about whether ideas can be objectively worse or better, and which ones. Keep arguing about that.
One of my favorite quotes:
Great people talk about ideas.Variously attributed, in various forms, to Benjamin Franklin, Eleanor Roosevelt, and others.
Average people talk about things.
Small people talk about other people. - Anon