This is a great thought. Upvoted! A nickel for your thoughts haha.

I will definitely use this as a post idea. Here's my initial take. A struggle does improve our happiness level. As humans we're programmed to return to a base level of happiness. If your radical rat Rufius dies, you will be really sad for a couple weeks. Then you will recover and return to your base level.

If you win a million dollars you will ball out for a few weeks and then get bored. You will come back to that same level of happiness.

Here's what I think a struggle does; it resets your base level of happiness.
Say you win that million dollars, you play with the money for 2 weeks, then you are forced to go shovel poop in the sewers for 2 weeks. Then when you come back to spending the million dollars you will be stoked on it again. You won't just get used to the pleasure. You could go back and forth between the 2 and always appreciate the money because it is separated by a struggle.

This is why you see rich people get bored and unhappy. They don't intentionally reset their base level of happiness. If a rich person were to go sleep in the woods and live off the land for one full week every month, they would enjoy their mansion more. Instead they just try to buy more happiness by improving their mansion and their material wealth. This doesn't work. It needs a reset, not more spending.

It's all about the struggle.

Dang! Thanks for spurring that thought. Picture me grabbing my camera and shooting a video on this right now.