My good friend Rodney recently asked me to explore this question. It's been on his mind, particularly following an experience wherein a woman he'd just met told him she didn't want to know anything about the contents (or the supposed health impacts) of the hot dog she was offering him, since that knowledge might compel her to change her hot dog consumption habits. She chose to ignore a recent WHO-backed study linking habitual consumption of processed meats with a higher incidence of colorectal cancer. Surprise! Old food isn't as healthy as fresh food. Imagine that!
Was she on the path to bliss? I get the feeling that Rodney doesn't think so. I tend to agree with him. This sort of chosen or forcible ignorance doesn't seem pointed toward bliss or happiness in the long run. So is there any truth to this adage with which we're indubitably all familiar?
It strikes me that there may be a semantic issue with this adage. And before you decry a semantic analysis on its face, please remember that you've chosen to read words, and that semantics connect those words with meaning. Are you looking for meaning?
A clear stream of meaning flows from language that follows agreed-upon rules of syntax and grammar, and that uses words in a historically consistent manner. To help with the latter, etymology extends a steady, patient hand.
The word 'ignorance' stems from the verb 'ignore' which harkens from the Latin 'ignoscere' that once meant "to not know". Would you say, "Not knowing is bliss"? And even then, do we conflate 'bliss' with happiness too easily? Perhaps bliss is mostly accurately the type of happiness that results from ignorance. Or perhaps bliss is a momentary flash of happiness that doesn't necessarily include a long term benefit. Early in this exploration, I think it's more possible that "surprise is bliss", or "serendipity is bliss", or even "the unexpected brings bliss".
There are those expectations again. They keep cropping up of late, especially in my discussions with friends about happiness and its precursors. In my own experience, many of the unhappiest and most disappointing moments in my life arise in close proximity to unsatisfied expectations. I might go so far as to say that expectations preclude bliss.