James linked to a slightly painful story about how badly a product demonstration can go wrong:

In the programme, Mercedes drives 3 S-classes behind each other. The first car hits the brakes, and the two following cars brake down automatically, to avoid a crash. In theory. In practice, the first car braked, and the two others continued right into the back of each other, resulting in a 3-car pile-up at the test site.

According to a German news site, the blushing Mercedes security engineers soon discovered the problem: The test had been done in a hall which was made of steel. This confuses the radar, and the system doesn’t work properly, causing more than £150,000 worth of cars to crumple into each other.

The system “works perfectly in all other circumstances”, according to Mercedes.

There’s a rule that says every time you demonstrate your product in public, however well rehearsed you are, you’re going to find at least one new bug. At least we only have to worry about the software crashing.

Product Demonstrations and Murphy's Law