With this post,
rillaspins reminded me of a bit about the water dispensers at work. We used to have the typical water cooler with the 5-gallon or so jug that would need replacing every day or two. Then a while back we got these gadgets that filter the city-supplied water into something that doesn't taste as miserable as city-supplied water.
These dispensers have three buttons. One button is blue. Two buttons are orange. It was obvious to everyone that the blue button resulted in cold water being dispensed. That was no problem. What was a surprise was how many people didn't realize that both orange buttons had to be pressed to get hot water. I can understand trying one button, then the other, then both, but it came as surprise that the simple safety feature had to be explained to some. It is a safety feature, too. The hot water is steaming hot - I don't need to bother microwaving the water for hot tea.