I disagree.Originally Posted by demoiselle
"I didn't fail to notice him" is NOT the opposite of "I failed to ignore him"
"I didn't fail" is the same as "I succeeded"
"I didn't fail to notice him" is the same as "I succeeded to notice him" or more simply "I noticed him".
"I failed to ignore him" means "I tried to ignore him but I couldn't". In other words "I noticed him".