I think this is a per-person issue. I personally am a “I need to care deeply about what I’m working on” kind of person; I’m not motivated by problem-solving for its own sake. Some people are. I suspect that there are many successful entrepreneurs in both categories, but the kinds of problems they solve and the kinds of companies they build are likely somewhat different.
I'm both. I need to deeply care in order to work on it at all and I also need to regularly pivot and re-evaluate. The two go hand-in-hand: the frequent pivoting is how I discover something that I both deeply care about and which I think there might actually be demand for. It's like an evolutionary exploration algorithm.
Like the parent wrote, I think "deeply care, but no viable business plan/market" is a very common failure mode. You need to kill your darlings. Caring deeply is a very necessary but very much not sufficient condition for me. Also, you'll end up caring about something even more if way more people care about it and are happy to have found your product/service. Like how you'll care about cooking even more if other people are happy to eat your food. It's a mutualistic cycle.
The main downside is this can lead to extreme indecisiveness and uncertainty and instability; but I've decided to accept this risk in the trade-off against the risk of building a ladder against the wrong wall.
