It does not appear that this is a direct quote from any other media. However, it is reminiscent of a quote about Batman (another DC Comics superhero) from The Dark Knight:
"He's the hero Gotham deserves, but not the one it needs right now." —Commissioner Gordon
In both quotes, the hero is said to not be the one that the people need, but the one they have got anyway.
This may just be a coincidence though, as it is a fairly common trope for the hero to doubt that they are the one that the people need. For instance, Oliver Queen has had these doubts many times on Arrow. Stein's response is a typical response of "You are better than you think you are" (warning: TV Tropes link), saying that the hero must be the one to save the day.