All construction guys have a pile of extention cords somewhere they been meaning to fix or get rid of. Just saying
And a lot of those are because the cords got stretched. They rely on the strands of conductors for their strength and their own weight will stretch them (making the individual strands thinner and less able to carry current) if they're left hanging or if they're stressed, like if someone trips over them and pulls them. A couple of strands are so thin they overheat and melt, then all the current is put through the remaining strands and that overloads them. Extension cords are good for what they are, but you have to be careful about how they're used and treated.