Well just look at the blunders made with the european gps satelites this year, two came in the wrong orbit due to a probably russian software failure. Look how many times this had already been done succesfully , tested and still some error occurs, now if you make a comment about that I would partially agree, this should not happen unless an accident occurred.
But still it did and often does which tells me this is science at the cutting edge, they don,t call it rocket science for nothing.
But this mission was even more unique, a one of a kind, the thing has been out there for ten years and travelled 6.4 billion kilometres , the rendez vous was a succes and they even landed the lander on the comet with some glitches yes. Two things did not work, out of, what? two thousand things that could have gone wrong? They gave it a 50% chance from the get go.
No I can only be very silent on this achievement in awe what they did achieve and so are other space organisations that congratulated ESA on this achievement.