You have to get the timing right. Otherwise you land in front of the truck and become a greasy spot.
Yup, timing. That's why, in that UPS TV commercial, the girl checks her watch before blindly falling backwards off the building and onto the top of the passing UPS truck--right on schedule. Oh, wait...I think I hear the UPS truck coming down the street. Gotta go, I have a roof to catch! <img src="/images/graemlins/smile.gif" alt="" />