People get in each other's way.
People pant after different goals. Sooner or later our paths will collide, twisting metal or emotions or relationships or schedules. You are meeting friends for a seven o'clock movie, and work had kept you later than you'd planned. You had run home to quickly change clothes, and now almost to the theater you remember that you hadn't had time during the day to pick up any cash. The banks are closed, your ATM card is in your planner, but your checkbook is in the glove compartment.