(LEAD) 'Oh Hae-young Again' heroine shares theory on show's popularity

(ATTN: UPDATES with more comments at bottom; ADDS photo)By Park Sojung

SEOUL, May 16 (Yonhap) -- Actress Seo Hyun-jin, who plays the humble and relatable heroine of the popular cable series "Oh Hae-young Again," thinks she might know what's turned t