Hmmm. well, a couple spring to mind...

As documented here, I bought and tried a number of lighters with built-in compasses. They ranged from $5 to $75, from no-name Asian knockoffs to some of the top names in lighters.

I wasn't expecting much- I don't smoke, but was carrying a lighter on general principles, and for the occasional gallant gesture. The only thing I often needed a compass for was orienting myself when emerging from the dark labyrinth of the local subway system into unfamiliar city streets- a general idea of where north was would be fine.

But not one of the lighter-compasses pointed north. Some just moved around randomly, some always pointed to the same point on the lighter, and some were shipped with enormous bubbles that kept the dial from moving freely. All were completely useless.

Then there was my first real try of a Marmot Mountain Works "Burrow", a tiny, expensive little Gore-Tex one-man tent that's little more than a bivvy sack with a hoop at the foot as well as the mouth. It was my first, and, as it turns out, my last Gore-Tex tent. I knew the ventilation between the mouth of the tent and the little "eyelid" window at the foot wasn't going to work when I noticed that the mummy bag, with me inside, plugged the diameter of the tent completely at about rib level. However, I was more disappointed to wake up in the morning in a sloshing pool of condensation. When I got out of the tent, I saw that the whole thing was covered with almost a quarter-inch of glaze ice from a full night of freezing rain.

Well, "duh", you say, of course no fabric is going to "breathe" when it's encased in ice...

Yeah, but a tent with an old-fashioned fly would have worked fine.

In it's defense, I used it for a couple of long backpacking trips later, and it did fine under more common conditions... but it was an interesting (and expensive) lesson on overlooked limitations.

I'm sure others failures will come to mind, but, mostly I wanted to say.. good question!