So yes, that's not what I was saying, but it's true I also suffer from RIDICULOUS time-optimism. When I say I'll be there in 30 minutes, that's what I honestly think.
But I forget about the time to find my always-lost cell phone, the time to ride the elevator - basically everything except the actual time on the road/bus/etc... 30 minutes being that magical time every light was green and everything went perfectly, etc.
This impacts all areas of my life. It's a reason I'm reluctant to carpool or take caltrain, heck, I'm always late to my Therapist... and I pay a lot for that.
Point is that I really try to avoid things where I have to be EXACTLY ON TIME.
For instance, if I'm going to a theater show, I'll plan to meet my friends for dinner beforehand. I might not be able to eat (they will), but at least I'll make the show on time.
Incidentally "I'll plan to be 30 minutes early, so I won't stress the entire time"... doesn't work somehow.