"ignorance is bliss" is a very good saying and one of my favourites.Its translation in Latin is something like " ignarus est bliss".But its original is still more popular.
How Do You Say "Ignorance Is Bliss" In Latin?
The Latin word for ignorance is 'inscitia' and bliss is 'felicitas' but you'd be best to get some final clarity on how the actual phrase goes before committing to a tattoo.
