もとはといえば
when it comes to the cause; when you get right down to it; as for what started it; as for the reason
Also written もとはと言えば
Expression
元もとはと言いえば、健ちゃんが鈍にぶちんなのがいけないんだからね～っ。
When you think about it, it's all Kenny's fault for being so obtuse.