Yea, but happiness is a weird thing. After live changing events, both positive and negative happiness is impacted for a while, but after a couple of months most people gravitate back to their default happiness level.

I would have assumed the more intelligence you have the more capacity to understand and worry about problems you would have.

Intelligence gives you the ability to understand these things, and can also give you the understanding that worrying about the things you can't change is of no benefit and the ability to then put those things aside so you can focus on changing the things you can improve.

That doesn't always come naturally, but it's a valuable thing to practice.