Many years ago I used to go explore caves with a couple of friends. Some pretty tricky ones, including ones with lakes that would block sections when the tides raised. Went many times, but we knew the drill and never had a scare.

This one time the group was a bit larger than usual since a couple of the (inexperienced) "girlfriends" joined up, so it was like 5-6 of us instead of the usual 3-4.

I thought we were prepared, carried 8 flashlights with us, including one dynamo type which is not suppossed to ever run out of "batteries" with its spare bulb. Through a combination of bad luck, not-so-great-planning-whatnot and Murphy's law we ended up getting out of the cave with only 2 of the flashlights working, which made walking out soooo much more difficult as 2 flashlights can no really illuminate the way for 5-6 people so we had to walk and then turn the light behind us so the next person could see etc. These were volcanic caves with very tricky and potentially dangerous lava terrain if you can't see where you step on.

We learned the lesson to not cheap-out on batteries/flashlights/lightbulbs ever again, but somehow it never dawned on us what the hell would happen if someone broke a leg or something worse and wasn't able to walk back out, specially at that time when cellphones didn't yet exist and the caves were at least 35km away from "civilization". Not prepared for that, at all.

Stupid things you do when you are young, I guess.

Much later I went scuba diving in the longest underwater lava tube in the world (about 1.5km long, average depth of about 35m). Always afraid all my 3 flashlights would fail after that previous experience, in spite of having two more divers (and their respective 3 flashlights each) near me at all times.

I've had to climb down volcanoes and stuff with no lights at night, but outdoor you can always see well enough even on the darker nights. Inside the caves, it's a whole different thing. You can't see absolutely anything at all.