hmmm... maybe I missed something... but I didn't get that.

I still keep thinking
Strength: how much force it takes to bend the steel.
toughness: how much deformation before the steel breaks.

maybe it's overly simplistic... but I think for the most part it's accurate...
and I don't want to over think it too much... (even though we kind of already have started)

EDIT: this was reffering to bld's post.

also knotslip, yes, very true.
that's why a knife CAN be TOO tough...
If it has some strength too, then it will spring back after deformation better won't it?