...but it does.
I thought I'd fire off a quickie, just had to use a little piece of kitchen wisdom my mother taught me.
If you have a jar that won't open, turn it upside down and bang it against a hard surface a few times. If it still won't open, repeat.
I believe it works best or only with glass jars that have metal lids - like on jam, or in my case, applesauce. But I seem to remember doing it with a mayonnaise jar or a peanut-butter jar, plastic-on-plastic. So who knows.
As to the possibility of breakage, I've thought that too. But I've never broken a jar or seen one broken doing this. You don't have to hit it very hard.
On the same note, most beverages you're supposed to shake well before drinking (I do this with Sobe drinks) can be stirred up by smacking the bottom of the bottle. But this only works right when the cap is sealed and unbroken.
I think it has something to do with pressure and physics.
Alternatively, if you have a stubborn jar... I don't know that they make them anymore, but antique shops might have them. My mother has this handheld device from the 1950s that you open by turning to the right, you put it on a jar and turn to the left, and its claws close around the lid. When that happens, you keep turning, and it's trying to tighten the claws, so that force plus your own strength opens the jar. That thing never fails, when pounding the lid doesn't work.
Expect more blog posts under this new 'Food' label. I love to cook all kinds of food. My wife and I are both fairly picky, but I'll make something even if I don't feel like eating it, if Jen wants it. Like last night, but that meal deserves a topic of its own - I think it's both of our favorite food...