Is it enough?
Even doing "everything" is not the same as doing it successfully. All we can require is serious efforts of specific sorts; we cannot require success. And the impossibility of success is necessarily an excuse - given serious effort, an entirely satisfactory excuse - for failure. To refuse to accept the excuse is to refuse to regard the defendant as a moral agent: for it is in the nature of moral agents (of human beings) that their best efforts sometimes fail.
~Michael Walzer, "War Crimes: Soldiers and Their Officers"