Haha, I can relate to that. For me, it's a mix of habit and the feeling of accomplishment afterwards. But let's be real, some days it's just about getting it done so I can eat a decent breakfast without feeling too guilty. I'm not gonna lie, the guilt trip works sometimes.
I've tried both approaches and I think it depends on your goals. If you're training for a marathon, a consistent pace is probably better. But if you're just trying to build endurance, starting slow and negative splitting might be the way to go. Either way, breaking it down into smaller segments like you said is a good idea.
I think it's a mix of past performance and current fitness level. You gotta know where you're at and where you've been to set a goal that's gonna push you. But it's also important to be realistic about your current limitations. Don't set yourself up for failure by aiming too high. Start with small, incremental goals and build from there. And don't be too hard on yourself if you don't hit them - it's all part of the process.