I think the former leads to the latter. I can't count the number of times I set myself up to do a ton of different projects at once, only to end up slowly parin

I think the former leads to the latter. I can't count the number of times I set myself up to do a ton of different projects at once, only to end up slowly paring it down to just whatever the most critical project was and spending more time than the entire estimate for the rest of the projects on that one thing. If that happens to you enough times, you'll start to extrapolate the pattern to long-term estimations of what you can do and it can really mess with your self esteem. Interestingly, I find this only happens with personal projects. At work I just overestimate everything to protect myself. So, it may also be that for things outside of work I simply underestimate how many of my life resources (time, energy, willpower) are eaten up by work and that confounds my estimates. I'm honestly not sure which thing is the bigger factor.