We were climbing on my 30m rope I normally use indoors. After climbing some walls in the main area we decided to move area to take a look at the taller walls. I knew the rope was not long enough for the tallest walls, but judged it would be sufficient for some of the shorter walls in this area.

We discussed the risk that the rope might not be quite long enough. To be safe, we tied the dead end of the rope off to the rope bag. I was climbing. We agreed if the rope was not long enough for me to be lowered to the floor, it would only be a metre two short, I could be taken off belay and safely downclimb. As I'd expected, the rope was long enough and I was lowered to the ground. We swapped over and my partner completed the route.

We now "knew" that although the rope wasn't long enough for the tallest wall, we could use it for some of the walls in this area.

We looked round for another route and decided to do one on the wall behind us. I led it. As I was being lowered down, my partner suddenly stopped me. I looked down and he was holding the end of the rope in his hand with only a few centimetres spare. I was still 3 or 4 metres from the ground. I grabbed on to the wall, convinced my belayer to let the rope run all the way out of his belay device, and down-climbed to the ground.

I was lucky that my belayer saw the end of the rope in his peripheral vision and grabbed it before it went through his belay device.

Our eyeballs must have seen it, but our brains had failed to register that the ceiling stepped up, and this wall was taller.

If I recall correctly, there are signs about checking your rope is long enough, but we dismissed them because of sign-overload and because in our minds we had already checked the length of our rope.