Marriage may not be a business, but it's a huge financial commitment and worth being clear about up front.
Also, nothing is ever 100%. If you wait till you're 100% on ANYTHING, you'll never get anything accomplished in this life. No one is ever 100% ready for marriage, 100% ready for kids. And if they think they are, they're kidding themselves or totally unaware of what they're getting themselves into!
My stepkids believe they're 100% ready to take on adult decisions such as sex, partying all night, choices on college and sports and whether or not to do homework. THier mother encourages them to be 100% making their own decisions and refuses ot exert her discipline as a mother. As a result, these 14 & 16 year old kids are failing in school because they forget thier homework, staying out all night, exhausted all day, and clearly going to get into trouble sooner or later (and my husband can't convince them that it's not wise to let them jsut be this unsupervised on a regular basis).
They think they're 100% ready to make these decisions becuase they have no idea of the consequences of the decisions. They dont' have the background or life experience to have a clue of the consequences of their decisions.
If you ever think you're 100% on something, be afraid... be VERY afraid... you're probably missing some vital information, like my stepkids are missing vital information on the consequences of their decisions.
I say it's much better to have your eyes open and financial expectations clear before you walk into a marriage, to acknowledge that it's not always 100% and may from time to time require discussion, compromise, etc. A prenup provides clearity to this.