Regarding Jane Austen's Pride and Prejudice, the adage "Desperation is the surest path to making a decision, good or bad," means that when one is desperate and is forced to make a decision in haste or due to extenuating circumstances, a decision may be good or bad because a form of anxiety has pushed the issue.
We see this is when Lydia and Wickham run away. At first this is concern by the family that they may have married, but then there is real fear that, in the face of scandal, they may not have married. The desperate choice on Lydia's part is not a good decision, but there is hope that it may be "fixed" if they have at least married to avoid Lydia's reputation being irreparably damaged.
Elizabeth receives a letter from Jane that reports Lydia's "desperate" act:
By this time, my dearest sister, you have received my hurried letter; I wish this may be more intelligible, but though not confined for time, my head is so bewildered that I cannot answer for being coherent. Dearest Lizzy, I hardly know what I would write, but I have bad news for you, and it cannot be delayed. Improdent as marriage between Mr. Wickham and our poor Lydia would be, we are now anxious to be assured it has taken place, for there is but too much reason to fear they are not gone to Scotland...
The reference to Scotland is Gretna Green, a place outside of England where young people could elope and be married immediately. With marriage and the consummation of the marriage, a young woman and man could avoid their parents' refusal to give their blessing to a marriage at home.
In this case, ironically, the desperate move to run away and be married is no longer the worst that could happen; if they ran away and did not marry, Lydia's reputation would be so damaged, that making a good marriage for her would be impossible.