I'm a fairly optimistic person and I run into the missed deadlines issue with anything non-work related with some regularity. I underestimate the amount of time something will take me or overestimate my ability to start the task.

At work, basically, if there is a monetary value attached to the task, I have no issue. I've tried to analyze this but it seems to come down to things that I don't really HAVE to do will get pushed because I'm optimistic they will work out, as they have in the past, and if they don't then there is no real consequence. Those that are work-related have a direct consequence, less income, so they feel more critical. I'm not a developer so it's easier for me to draw a line from my work to monetary value but this may be a perspective to bring up if you are working with a similar personality type in the future.