In The Tyranny of the Ideal, Gerald Gaus draws attention to a trade-off faced by anyone pursuing an ideal conception of justice. What he says here seems almost trivially obvious (at least once he puts it down on paper), and seems to have obvious implications (at least once one sees it set out in print), but I still find it insightful. He calls it The Choice:
The Choice: In cases where there is a clear optimum within our neighborhood that requires movement away from our understanding of the ideal, we often must choose between relatively certain (perhaps large) local improvements in justice and pursuit of a considerably less certain ideal, which would yield optimal justice (Tyranny, p. 82).