Just a tiny error, so tiny, just the thermostat that kept heating the liquid oxygen, just some forgotten procedure that someone forgot to cross-out from the check list, enough to cost a dream being shattered and can never be achieved again. And how Hollywood depicted almost everything accurately (bear in mind that the tag line, "Houston, we have a problem", was never spoken by Jim Lovell).
Human can do so many but He is the one who has the final say.
I never thought of shedding some tears while watching it. Reminds me of the Almighty.