You’re waiting for a bus that leaves the terminus at 8:10am. It should (by any reasonable estimate) reach your bus stop at 8:20. It is 99,5556% likely to be at least 10 minutes late. The probability that it won’t arrive at all is very good. Your watch is 8 minutes fast. Your cellphone is 5 minutes slow. At what time can you be sure that the bus is not going to arrive and you therefore give up waiting for the bus?