I’ve been thinking about this. Answers?
Err... The phrase 'ignorance is bliss' is sarcastic. 'Ignorance is bliss' in the sense that one actually believes that the ravenous bug-blatter beast of traal will not eat us if we put a towel over our heads. The phrase is invariably used as a way of chiding someone for being willfully, stupidly, or naïvely ignorant of the way the world actually works, such that the person stumbles around in a thick cloud of false confidence and superficial contentment, awaiting the inevitable, painful prat-fall.
People seek knowledge, because knowledge gives us fundamental understandings of the world that allow us to steer a course around and through problems and obstacles. It gives us a far more honest and real sense of confidence and contentment.
I have a different opinion. The maxim ignorance is bliss can be used in a sarcastic vein, but it's actually very truthful.
Your question overlaps philosophy and psychology. Look up "cognitive dissonance," for example. Do doctors and government always tell people the truth? Of course not. Politicians often lie for sleazy reasons, but there are situations where they may genuinely lie for the public good.
As a political activist, I learned long ago that truth can be a painful thing. Life would be so much more pleasant if I really believed I was living on an unspoiled planet, surrounded by mature, ethical people.
Unfortunately, the global environment is in rapid decline, and even the people here in "progressive" Seattle nauseate me. So what can you do?
Of course, it's very hard to fix problems without knowing the truth. That's why those of us who want to fix problems may have to endure the bitter slings of reality while our apathetic neighbors blissfully party the night away.
There's also a personal dimension. Do you want to be an ignorant person? Some people are perfectly content to remain in an ignorant state; some actually boast about it. But, for others, embracing truth is a matter of pride and dignity.
Nevertheless, it's hard to imagine how anyone could face a solid wall of reality 24/7 without going crazy, or at least feeling depressed. That's why people engage in "escapism," whether it's taking a walk in the woods, daydreaming or fantasizing about a better world.
In summary, it's a balancing act. The pursuit of truth is a noble activity, but it can be surprisingly dangerous.
Beware that, when fighting monsters, you yourself do not become a monster... for when you gaze long into the abyss. The abyss gazes also into you. -- Friedrich W. Nietzsche
To expand on Conifold's well-informed answer - some knowledge is painful. The poem points out the ironic fact that not knowing ones fate allows one to live a better life.
Examples include knowing what people really think about you, knowing why and when a relationship will end or when you will die. In cases like these, it's often better (smarter) not to know. And that's not because it is not useful information - it would be VERY useful but for our emotions over-riding rational responses to the knowledge.
Interesting question. Thanks.
Even if the premise is true, humans don't necessarily do whatever maximises their personal bliss. Insofar as philosophy comments on this, the question is what construal of our ethical responsibilities we try to live by, when we can bring ourselves to do so. Doing what serves our personal bliss sounds closer to egoism than any other theory of ethics - a 1-person consequentialism, as it were. But people often prefer consequentialism in a more holistic sense, possibly not even limited to fellow people. Or they may act out of a sense of duty, or may consider knowledge or critical thinking a virtue. And whatever we think as individuals, it seems our societies tend toward progress rather than short-term pleasure. The unitalicised hyperlinks are to four major philosophical accounts of ethics.