sentences:  Daksha(the prajapati - one of the eight manasputras of Brahma and a stauch Vaishnavite - Vishnu happens to be his grandfather in vasthu roopa) was against this marriage because Shiva had beheaded Brahma(Daksha's father) and being Moola-purusha Shiva actually didn't follow any rules(As he was nirguNi) designed by Daksha which made him not to belong to any of the class-categories classified by Daksha(being a Prajaapati, it was his duty to classify everybody from Lord Vishnu - to smallest organism)) and hence bore enmity with Lord Shiva; He married his favouritest daughter Sati to Lord Shiva after multiple insistence from his aaraadhya(celebrated) Lord Vishnu and his father Brahma.Added to this enmity Lord Shiva after marriage, did not do proper conventional(Conventions designed by Daksha in his Shaastras) reverence which is to be done by a son-in-law to his father-in-law, instead Lord Shiva blessed him for Daksha's prosperity; which yet enraged Daksha's ego, so he decided to perform a mahaayagna to which he invited all except the Aadipurusha Lord Shiva himself.In vasthu roopa since Sati was Daksha's favourite child; she couldn't refrain from attending her father's greatest of yajnas.