what does "tip over the edge"mean? Landry contemplated Strike with what seemed to be surprise and disfavor. “You were at Blakeyfield Prep?” “Briefly. Before my mother realized she couldn’t afford the fees.” “I see. I did not know that. Even so, perhaps you’re not fully aware…John has always been—let’s use my sister’s expression for it—highly strung. His parents had to bring in psychologists after Charlie died, you know. I don’t claim to be a mental health expert, but it seems to me that Lula’s passing has, finally, tipped him over the…” “Unfortunate choice of phrase, but I see what you mean,” said Strike, writing Bristow off rocker. “How exactly has John been tipped over the edge?”