Ah okay. It seems we fundamentally disagree about my point #2 because of a meaningful difference in semantics. You use "I care about X" as a statement about the externally-visible operations of the speaker. A nurse cares for patients even if she is tired, achey, and annoyed. If you will, "caring" is a property of a one-person system's public API.
I use "I care about X" to be a statement about the internal state. "I care" is a description of emotions and motivations. So which meaning is correct?
Well... its semantics, so no "correct" in the same way that there is a correct measurement of the gravitational constant of earth at sea level above average-density crust. I like to say "All models are wrong; some models are useful", and the purpose of words is to communicate. So which definition is more useful? I assert that it depends on your time horizon and your ability to convey relevant insights.
In a short time horizon where OP doesn't know what this guy's problem is, your definition is more useful for deciding how OP should act. OP has little way to open a heart-to-heart conversation where the cofounder can open up with his worries or commit to starting on a path to change his habits. OP probably doesn't have time to wait for the cofounder to change his habits unless they sit down and rigorously design those habits and the communication protocols to reinforce them -- something I've only seen from my wife and I. In a short time horizon, OP has to deal with his or her cofounder as-is.
So why am I still blathering on?
Because reading "he doesn't care" struck a nerve. I've been "the dev (or student) who 'cares' about his work but not enough to overcome procrastination" for multiple chunks of time from 2004 into early 2017. What changed wasn't my level of concern for productivity but instead several types of growth:
- Getting access to tools that allowed me to block distractions.
- Developing good habits of diet, exercise, and especially sleep (and escaping from a uni culture which said "sleep is for the weak")
- Learning skills of breaking down projects, insisting on understanding the 'why' of projects, asking well-structured questions, and planning out steps to execute.
- And 14 months ago, learning what discipline even actually was and how to build that muscle.
This growth all happened over the course of a decade of trying to debug myself which included 4 PIPs and 3 firings, so quite a long time horizon and empirically a longer time horizon than anyone but my wife could reasonably have had the patience for. If you had told me during this time that I did not care about my work, I would have been internally seething with anger, but not even known how to counterargue. So just so you know, concluding that about someone can be rather inflammatory to them.
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By the way, thank you for answering me. Writing that all out was really useful for me. If you'll humour me again, I'm curious: What are some ways to tell that you don't love another person? What is love? When I've asked about this sort of thing before, I've just gotten the response " Baby don't hurt me; Don't hurt me--no more ", which is unhelpful.