1. People don't actually know how long it takes to get places, meaning that maybe this one time they got from here to there in twenty minutes and therefore in their minds it takes twenty minutes. This is sort of like bowling a 212 once and then claiming it's your average. Twenty minutes was a fluke. A little over thirty is normal.
2. People round down. That "twenty minutes" was actually twenty-two minutes and that "a little over thirty" is actually a little less than forty.
3. People think things take "no time." Everything takes time. Putting on your shoes takes time. Finding your keys, your wallet, and cellphone, turning off the lights, turning off the coffee pot, putting on your jacket, patting your pockets for the keys, wallet and cellphone, locking the door, walking to the bus stop, forgetting whether you actually turned of the coffee pot or just reminded yourself to turn off the coffee pot, slowing down your walk as you debate whether you turned off the coffee put, further slowing as you debate the possible harmful effects of not having turned off the coffee pot and whether it is worth it to turn around and check, turning around, unlocking the door, checking the pot, finding that you did turn off the coffee pot, locking the door again, debating whether the fact that you went back and checked was a determining factor in whether the coffee pot was on or not, coming to the conclusion that if you had not gone back and checked to see if the coffee pot was on it would have been on... it all takes time.
4. People think they are there before they are there. Someone says they are going to meet their friend at the Harvard Bookstore in Harvard Square at two o'clock. They get off the redline at two o'clock and think, "I'm here." But it's still another five minutes walk to the Harvard Bookstore.
5. People are overly optimistic. I've been called a pessimist by a number of people, but things do go wrong. Buses are late. For some reason there id someone is getting on or getting off the bus AT EVERY SINGLE STOP. Traffic is congested. You get lost. People give you bad directions. None of these things are the end of the world, but they do happen.
But really, I'm not sure how relevant any of this is. I think that most people are on time for work. I think most people are on time for job interviews. I think most people are on time for plane flights. If something is important to them, people will be on time.
And if something isn't, they won't.