When BA came out with the new weight sums but said it was okay as long as you could put it yourself into the overhead (to keep cabin crew from masses of heavy weight lifting that could knacker a back--which seems fair enough) it shows how detached policy makers can be from the actual people involved.
If you are short or even moderately short (i'm 5'4") or less, and you have short arms as well, it's nearly impossible to lift and put a carry on of any weight or size up and into a 777 or bigger plane's overhead bin! It could be 2 kilos but it's the height getting it over that angle ledge that's the prob.
If one is 5'0" as is a friend with whom I often travel, it's impossible. I always help her. Or someone taller than I am helps. She cannot even reach any part of the bin.
So in the end weight has nothing to do with it. It's the heights of the overheads on the big planes that make it difficult if not impossible to breach.
But of course BA has to have a policy, so fair enough that they say if you can "do it yourself" then okay. Not sure what else they could say.
I find buddying up with other women when I'm traveling alone is the answer, if cabin crew either don't want to help or cannot help because they are busy. If I see someone on the short side struggling I lend a hand right away. And sometimes a male pax will give it a boost.
And quite often especially young male cabin crew rush over right away to give it a boost over the ledge if they see you on tip toe struggling. Bless 'em.
So the weight thing? That's secondary to Short People!