He planted plain old paranoid self-doubt and insecurity.
Osiris: "the reason your wife didn't try to get your help to solve things is because she KNEW you are useless, and you are useless because the only way you were ever strong was by borrowing MY power"
And NO, it didn't fail. It worked WONDERS
(Seth *is* cutely naive... and gullible, after all)
BTW, part of the reason it worked is because Seth himself (apparently) remembers shit about his own original past, from when he first ever became a god
Oh ok
I need someone to throughly explain the jinx Osiris placed on Seth. And what did he put in him? I thought it failed