When climbing on to the roof of your house, using a ladder that is too short by a couple of feet, and then discovering that the slates are slippery enough that you have to scrabble to get to the safety of the ridge, by which time you've forgotten where the now invisible ladder is, and going to the edge of the roof to dangle an experimental foot over is not an option, and your partner's gone out...
...erm...
...perhaps I started this at the wrong point.