An Unmonitored Toaster Always Scorches

Wednesday is "free bagel" day where I work. This means that all morning long, the cafe is generally inundated with the aroma of ... scorched baked goods. And it does not necessarily smell like victory, I can tell you that. I have observed this ritual long enough -- a little more than a year now -- and I have a question:

Why is it that "a watched pot never boils," but if you turn your back on a toaster for just a moment, you end up with something on the order of a roof tile?

A burnt bagel image lifted from Cakehead.com, who lifted it from the Museum of Burnt Food

I'll appreciate any thoughts my loyal Prophet or Madman-philes might have on this topic. I know others must have thought about it. It turns out that puffintoad beat me to it by a little more than two years.