Why reflectors don't work

With days getting shorter and shorter, and sunset coming earlier and earlier, we have more and more reasons to think about why cyclists need lights as well as reflectors when riding in dusk and dark:
If you go for a drive tonight, you'll see reflectors shining brightly from mailboxes. You'll see reflectorized stop signs. If bike riders are out, you'll see their pedal reflectors . All these reflectors will appear bright, and very easy to avoid.

So here's the seven million dollar question: If all these reflectors are so darn bright and easy to see, how come the bike safety nerds insist you need active lights to be seen at night?

There is a very scientific answer: reflectors work only under very specific conditions. Those conditions happen to prevail in most of the nighttime driving we do, so we get the impression that reflectors work most or all of the time. But reflectors don't work at all if those conditions aren't met, and many well-defined bicycle accident types occur in situations when we can expect reflectors to not work.