An electrician I once ran across had a picture of an aluminum ladder in his tool box. It was maybe a 30 foot extension ladder, and the top extension was bent at about a 30 degree angle.
When I asked about it, he said he had it propped up against a building to get up on a roof, and about 2/3 the way up, it started to bend on him, and kept bending until it came up against the wall. he said he was lucky because another fellow was on the ground under the ladder to steady it, and when it started to bend the guy on the ground was able to keep it vertical so he could hang on long enough to scurry down.
You can imagine his opinion of aluminum ladders. Me, I once went to use a wooden ladder and the first rung just broke when I stepped on it. I think I was about 16 when it happened, and it always made me nervous about wooden ladders.