Working backwards from where you want to be can give you purpose.
Most people are not working in a job they are passionate about all of the time. In fact, according to a recent Financial Times column by Lucy Kellaway, having passion for one’s job can be dangerous. One should at best care about and enjoy one’s job. But even the best jobs can get mundane and routine and it is up to the individual to make his/her career continuously challenging, interesting and fulfilling.