> People tend to look for more "balance" when they are unhappy with whatever their main focus is
I disagree with this. I'm simply unhappy working on any single thing for too much time, no matter how fun or interesting it is. It's having a few things going on simultaneously, and being able to switch between groups of people to interact with (where the null set is also one of those groups), that has always kept me happy.
Sometimes it's as simple as being tired of being around people, in general. Balance in this case means having some alone time. Sometimes it's just being frustrated and tired of computers and the internet, in general. Balance in this case means getting out and going on a weekend trip to a national park, away from internet access. Sometimes it's that you enjoy your work but you don't enjoy the way people at work treat you sometimes. It's not a dealbreaker or showstopper, but you need time with those few close friends that you feel comfortable around.
It's especially true when you work on a startup or anything else that necessarily involves not being your true self. I spend most of my working hours being what my teammates/investors/customers want me to be, not being myself. That doesn't mean I'm unhappy working on that focus, it's just mentally tiring and exhausting to deal with what's involved in turning that focus into a company.
I spend the rest of my time being my silly self and let my imagination run wild and invent freely without dealing with people, law, ownership, money, or any of that nonsense.
None of this means that I don't enjoy what my main focus is.