I think the title the grand optimist refers to his father. I think the cripple without a cane line is referring to the helplessness he feels from all of the complications in his life. The line about burdens not scarring his father seems to imply (for me anyway) that his burdens are scarring him greatly, despite them not seeming to effect his father. I don't believe, however, that the father necessarily left or treated the family roughly, but something definitely happened between his childhood and now to make him lose faith. Maybe (and this is just speculation), but I kind of got the feeling his dad was the guy who could handle any problem with ease, and he's talking about struggling with the complications in his life while constantly comparing himself to his mother, so I kind of felt like his mother was the one who was struggling and she eventually succumbed to the complications in her life. For me, I think that was the catalyst for whatever happened to make him lose his faith and resiliency, but I may be way off. Just a thought.