My own personal reflections, that I realize may not be true for everyone.

Hypothesis: Living in the moment and being content is a key aspect of happiness. The more you know, the smarter you are, the harder it is to live in the moment or be content.

1) The more you understand, the more problems you see.

When you understand little, everything is ind of random. You have minimal expectations. The more you understand, the more connections you make, the more you see how things could be and how far away they are from an ideal state. You focus more on the potential, and thus the future, than on the present.

2) The more you understand, the less novelty there is.

The first time you play video game in a particular genre (or watch a movie, etc), you take it all in and experience as it is. Little interactions are delightful, as your brain is happy to see two things make an unexpected connection.

After you complete a few, you understand how the system works. The balances and trade-offs that make up the nature of the genre. When you start a new one, you instantly start breaking it apart into a mental spreadsheet, rather than experiencing the literal thing in front of your face. The unexpected elements become expected because you know how even the unexpected stuff tends to work.

The more of life you experience, the less novelty there is to any part of it.

3) The more you understand, the easier it is to live in the future.

"I should try this", "I should do that". You get locked into intellectual responsibilities with long-term goals. The short term becomes just a nuisance to achieve long-term goals. You aren't only not living in today, you aren't even living in tomorrow, you're actually living 6-24 months from now.

4) The more you understand, the less of a point you see.

If you're a pattern solving machine, eventually you realize there's no bottom to find. There's always just another chaotic pattern to pick apart. Another thing to learn. The same things play out over and over again, mildly differently. You can't fix the majority of the problems you see. You can barely understand yourself.

You're good at min/max-ing problems. But what's the ultimate thing to min/max? You have no idea.

So you ask yourself, what's the point to the whole process? Simply maximizing brain chemistry? You know you can't just focus on happy brain chemicals because that will also ruin your life (ie, heroin).

5) The more you understand, the less you hope in magic.

Some optimism depends on magical thinking. "Maybe this will work out because X will happen!" Except X can't happen. But if you believe it could happen, you are genuinely more happy.

The more you understand, the more quickly you can solve all known aspects of a problem and get left with the parts that can't be solved. You know all the things that can't happen to fix a problem. The world isn't magical. Medicine isn't magic, doctors aren't magic, technology isn't magic, politicians aren't magic, problems don't just disappear over night.