No one predicted that the rover would break on day 91. They designed it to last at least 90 days. Between standard rocket-science safty factors and preparing fo

No one predicted that the rover would break on day 91. They designed it to last at least 90 days. Between standard rocket-science safty factors and preparing for the pessimistic end of all the uncertain risks, there is much room to go beyond your original mission. Imagine you design a bridge to support 100 tons. No one would accuse you of mispredicting if it holds up at 200 tons. They will accuse you of negligence if it collapses at 105 tons.