% for set over set?

Hey guys, i wa sjust wonderin how often a set over set happens and if there is any reason to ever fold a bottom set on a ragged board ?

i was playin a live game yesterday (.5/1$ blinds) and bought in for 10$. i turned it into 350-400 within a few hours and slowly dwindled bac tdown to like 150 - but then i hit a set of 4s and lost to set of 9s. do i just lose and say 'it was meant to be' or reanalyze and think of how i could fold? folding = -ev?