I have this theory that we feel the best when we choose to stretch our body or mind doing something that is difficult to accomplish. I think people are generally more happy when they're working on something useful or worthwhile. Yes, that includes time spent relaxing.
The retort is, of course, that we all hate work and want to go on vacation. I think the problem is the work we’re doing when we’re at “work.” A lack of worthwhile or important work is draining. Any escape from that is nice, but only for a time. Vacation becomes tedious once it becomes aimless.
We seem to be at our best when we’re deeply focused on some challenge and our minds seem to love it, regardless of the challenge.
When we dive into our work, we find joy in it and deep satisfaction.