In Jane Austens' novel "Pride and Prejudice", the main focus of all the women within the novel is to be married. It is an ideal that drives all the women in this story because to them without a husband around their arm they are worthless. Therefore if that is the mentality of society a marriage cannot be truly happy because a woman with marry because of stability not because of compatibility.
The most marriage fixated woman in the entire book is Mrs. Bennet, i can only assume that she may have come from nothing and been introduced into a little wealth upon her marriage. Mrs. Bennet is completely obsessed with finding her daughters suitable husbands and her husband seems completely annoyed by it. In fact the couple are so incompatible it is strange to imagine that they are married. Throughout the entire book Mr. Bennet shows no sign of affection towards his wife and Mrs. Bennet shows no sign of compassion for his opinions. They merely tolerate each other not love each other.
It is then no surprise that Elizabeth has developed this theory about difficult marriages. The signs of disadvantages exist within her very own household. For example Lydia's little stunt in which she elopes with Mr. Wickham. She obliviously is a rebellious child who wasnt properly socialized as a child which is one effect of a difficult marriage.
Which leads me to my next point although it is a proven fact that difficult marriages can lead to the children suffering both mentally, emotionally and physically. I do not think just giving up on the marriage is the answer because having a fragmented family is just as damaging to a child as a difficult marriage.
Thus my recommendation if you find yourself in a difficult marriage try to work things out but always keep up the "happy family" phasaud in front of the children. The children do not need to be involved in your adult trivialities. By keeping up the phasuad the children aren't affected untilt hey are old enough to realize and when they are of that age, the damge that a difficult marriage can cause is minimal for they are already mostly developed.
