Suppose you construct a ship that may take you to Barnard’s Star. Must you depart at the moment? Maybe not: Our civilization may create a sooner ship tomorrow that can overtake you on the journey. However clearly if you happen to wait too lengthy you then’ll merely lose out to an earlier ship. There should be some optimum ready time that can ship you to the star earlier than every other pilot.
What’s that point? “It has been proven that taking affordable estimates for progress, an interstellar journey of 6 gentle years can finest be made in about 635 years from now if progress continues at about 1.4% each year,” writes researcher Andrew Kennedy. “At this level, the journey may very well be made in 145 years.”
(Andrew Kennedy, “Interstellar Travel: The Wait Calculation and the Incentive Trap of Progress,” Journal of the British Interplanetary Society 59:7 , 239-246.)