Libra natives are always balanced; their decisions are wise and well thought-over. This is why the thing that horrifies them is the possibility of a mistake. No turn they take can be wrong; otherwise they will wear themselves down questioning every decision made in the future.
Thing is, Libra is too hard-working and concentrated to allow for a mistake. The possibility of one makes them feel that every effort they made was a waste. No one would want to feel that, right? Libras shouldn’t, too, as to err is human and mistakes only lead to personal growth and better judgment.