Why is it that people have such a hard time with such simple concepts? Reporters seem to get a free pass to be almost unbearably confused about subtle differences. What am I blathering about? I'm glad you asked!
Reliability is the idea that something will perform consistantly.
Trustable is the idea that something will perform how you expect it to.
So what is the difference? Well for simple things, things that people can understand just by looking at them, this tends to not be an important distinction. For complex things, things like computers or things built around computers, this difference gives people some trouble. Let's start by thinking about simple things.
I have on my desk a piece of paper, a pencil and an eraser. These things are all hopelessly outdated by the PDA which I carry about with me, but I trust them. Why do I trust them? Because over the years I have determined that these objects do what I expect them to. I also think of them as being reliable. Why is that? Well, for the most part they operate every time.
There are, without a doubt, some failures. Paper is not the most robust storage medium one can imagine for putting in a pants pocket and running through the laundry. Rough handling of the pencil will result in a broken lead. If the paper gets oily or I write too hard, sometimes it just does not erase too well. Depending on my mental model of what paper, pencil and eraser should do, these might be classified as trust issues, or as reliability issues. I have a fairly sophisticated model in my head of what paper, pencil and eraser do, so for the most part I think of these as reliability issues. I trust that if I run a paper through the laundry, it will come out useless. I trust that if I roll over my pencil with my desk chair it will afterward have issues. Since my mental model does a good job of predicting how the system will behave, and it is generally right, these are reliability issues.
I have in my living room a VCR. The clock on my VCR does not blink 12:00. In fact, every time I put a videotape in the mouth, I can watch it. Unless the tape is too old, in which case it might eat it. I have a mental model built up about that, so it is a reliability issue. Fine. But if I should want to record a show using the built-in timer functionality: Tough luck. The few times I did try to set that up, I ended up losing any semblance of confidence and just starting it manually on the slowest recording mode and hoping that the tape was long enough. That is a failure of trust. The trust issue is the most frustrating.
Software bugs, due to their complexity, tend to be trust failures. Software bugs that are simple enough to produce a useable mental model to compensate for are generally also the ones that get fixed. Because they're simple.
Prior to our recent election, we've seen computer scientist "e-voting experts" pontificate mightily about how computerized voting is not reliable. Well, the election went pretty smoothly. There have been some noteworthy failures, mostly in the screen calibration, but no widespread looting or anything like that. Why? The machines are reliable. That's why they were concieved as a replacement for paper balloting. The reliability of a direct interface is better than the reliability of marking cards or paper or something and then letting a computer count that.
So, now they'll quit whining, right? Wrong. Now they'll have to be a bit more clear about what they are objecting to. The machine's reliability is really pretty good. They're designed to keep backup copies of all the really critical data. The problem is that after being exposed to too much buggy software, these scientists just don't trust them to do what they're supposed to.
So, when bugs get revealed it only seems natural to distrust the machines, right?
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