I once was solo-ing around GG on a BPC Winch Weekend. I'd descended Mud Pot (this was before the traverse line was installed) and gone into Far East, and dropped doen to Mud Henslers. After threading through the odd chockstones, I got into the main passage, but, when I passed the first duck (under the stals) my light went out. In the dark, I fiddled, banged, tapped, prayed (etc) but the thing wouldn't work. Eventually, I decided to try and retreat ... blind. Funnily enough, this decision seemed to remove all the pressure - I couldn't see, but it was OK, I would just need to go slowly and carefully. Which I did. Back - under the easy duck, along, feeling both walls and slurring my feet carefully, threading back through the chocks, until, finally, I climbed up the slope back into the Far East Passage. Where I could see the lights of other caver, and (Sod's Law) where my light started to work once again!!!