All marriages fail, whether through divorce or death.
A couple has a better chance of going the distance if they have completed a prenup. It doesn't mean that you have to get one, but it certainly improves the quality of the relationship in the long run.
The reasons is because it allows a couple to openly discuss the common pitfalls that ruin marriages (finances, faithfulness, attitudes and values, goals and aspirations, etc.,) prior to getting married. Since there are a lot of examples already documented, a lot of the conditions can be cut, pasted, and modified to suit the couple's needs.
It serves as a mediation strategy that allows both parties to discuss these issues, and holds each other accountable to what they reveal; giving each party the right to decide if they want to continue getting married. When a situation gets close to an irreparable infringement, it can serve as an early detection warning and help to pull each other back from the edge.
If the relationship passes the due diligence process, then they would've caught the majority of problems before becoming bigger and more costly issues later on. If it doesn't pass due diligence, then it wasn't going to go the distance anyway.
When a person takes into consideration the inevitable, they would see that a prenup is nothing more than a tool that can be used for estate and family planning.