Why does time fly so fast?

Sometimes we never realize that time flies so fast. Just like me today. I woke up this morning and read my mails. Few minutes later, I made breakfast and took a shower. It was really refreshing. Taking shower in weekends is so different from in weekdays. On weekdays, I usually do it only within 10 minutes. Indonesian people call it "Duck or chicken shower." LOL. Don't blame me for not having more time. Weekdays are busy days.
After taking shower, I got some work to do related to my job. Then, I watched TV. Soon, I just realized that I did not do many things today and it's already 4 pm.
Oh well, I'd better start thinking what I'm gonna do later. Otherwise, today will just go like that.
pic: reslife.missouri.edu