This song is the musical representation of that feeling so many of us long for: complete and utter joy. Why is it so difficult to find? Because what no one tells you is to be really joyful, you need to be pig ignorant.
Think about the phrase “bundle of joy”: why do we use it to describe newborns? Because when parents first meet their infant, they are completely ignorant to the hell that is soon to follow. They hold the little creature in their arms, gaze into its vacant eyes, count its stupid little toes, and feel pure happiness. Twelve years later when they’re summoned for a court appearance, it’s unlikely that their child’s attack on that elderly gentleman with a limp is bringing much joy to their now desperate lives.
As understandably satisfied as I am with my own life, I confess that my moments of joy can be limited. When I look at my reflection in the mirror, I feel many things (awe, wonderment, reluctant sexual arousal), but joy is not one of them. This is because I am not ignorant of all that’s gone in to making me the woman I am. The knowledge of the pain and struggles of my life means that I, unlike the young man at three houses down apparently, cannot experience the ecstasy of joy just by gazing at my person.
Take a moment to reflect on the people who seem most joyful, and you will find they are undoubtedly quite ignorant. But don’t get confused: this does not mean that you have to be a total idiot to feel joy. The etymology of the word “ignorant” comes from the Latin ignoritsi, meaning “like a kitten’s brain,” and I am certainly not hating on kittens. Kittens are clever at many ways (mice killing) yet ignorant of others (chaos theory). This explains why cats look rather solemn when stalking prey, but purr like fools when they see a photograph of Henri Poincaré. By deliberately choosing to not understand that some orbits are not forever increasing nor approaching a fixed point, kittens find joy in dynamical systems.
This is why you will on occasion stumble across a topic on which I am not an expert on. These examples of my own ignorance are often the very things which bring me the most joy. I do not totally understand how jazz music or fruit pastilles are made, and therefore I can find joy in both. The same goes for black tar heroin. There is no shame in being ignorant of some things in this world; it’s all about pro-actively choosing which subjects are important to understand, even if that means sacrificing one’s own personal jubilation.
Given that the song was released in 1970, I am willing to excuse those hippies who believed that it was Jeremiah’s wine that made Three Dog Night so joyful. However, a less flower-powered analysis of the above lyrics highlights my very point—the line “never understood a single word he said” holds the key. Knowledge can be power, but sometimes ignorance is bliss.
Everyone Needs an Algonquin 
My dearest Aggie,
What can I say, you speak such words of wisdom they put me and my family to shame (he says in all modesty of course!) But I completely get where you’re coming from about kittens. Take my beautiful wife Philippa Middleton for instance (I know I have…heh-heh…sorry that should be Kate of course). But she is just like a kitten (apart from slaying mice that is) and indeed that is my nickname for her; Kitty Kat. But ignorant about chaos theory? Hmmm. I might have to disagree – there was certainly plenty of chaos left in the bedroom after we’d finished with it on our honeymoon (don’t get jealous my dear!!) Yet, I suppose, if you really want a good example of ignorant then one need look no further than grandad. Bless him, just turned 90 and when you think about it you’re so right for he’s had 90 years of ignorant bliss and is none the wiser as to how ignorant he truly is!
Anyway, must go my dear A, but I do so look forward to seeing you soon for some of that black tar stuff you mentioned. You know how much I am fond of a bit of treacle on these royal baps.
Love you as always,
Willy