Is it normal to be worried that my parents might divorce?

Before you vote 'yes', consider this: there's nothing wrong in their marriage. Unless there's a serious issue behind closed doors, they're doing fine. However I've heard of things that could put them at higher risk for divorce--for example, my mom was 20 when they got married, they're Christians, and both sets of parents divorced. They just recently celebrated 25 years, but I've heard of people being married longer than that who ended up divorcing. Is it normal to wonder about that when there's no reason to?