A few months ago I noticed that the light bulb in the recessed fixture above my office door was burned out.
No big deal, I thought: I removed the old bulb (it was VERY dirty, must have been there for years) to make sure I knew exactly what kind of bulb I needed. Fortunately, I had an identical spare.
I put the new bulb in: it didn’t work. Hmm, that’s odd.
I tested the new bulb in another fixture: it worked. Even more odd.
I then took a standard light bulb and tested the fixture above my door: it worked.
I then tested the old bulb in a desk lamp: it worked.
Everything worked. Nothing was burned out.