Taking off in a B737-800 a few years ago, we didn't get the chimes from the cabin to say that they were ready. I was listening on the flight interphone, so I knew that they were pushing the button. I assumed that there was a failure with the interphone system, confirmed verbally with the purser that they were ready & decided to investigate further once on the way.
At top of climb we didn't get the chimes with the secal check & it dawned on me that we had a 'aural warnings' problem. A quick check revealed that the aural warnings C/B was out. We had just taken off without a working Take-off Config warning! Fortunately the swiss cheese didn't line up that day & everything else had been done right.
The aircraft was fresh out of the hangar & the engineers had pulled the C/B & not reset it. Evidently it is common practice to pull the C/B to prevent annoying warnings while certain items are being worked on.
I filed a report, but the company didn't seem to be that interested & the information wasn't disseminated to the other pilots at the airline.
I don't know if the other guy checked the C/B's, but I found that my C/B preflight check was inadequate. The said C/B is behind the F/O, right beside the fire extingusher. If you don't move your head right over so you can look vertically down beside the fire extingusher, you can't see the first column of breakers, where it can be found.
Complacency can set in with time, particularly when "nothing is ever out of place". I have sat in a cockpit & heard a crew respond to a checklist with "down - 3 greens" when the nose gear light wasn't illuminated.
It taught me a good lesson & now I 'watch' myself more than I watch anyone else, particularly if I am tired or distracted.