You can say: The more a life decision scares you, the greater (or 'the higher') the chance that you need to do it. If you want to rephrase it, you can try different things but what matters is what you're trying to express. What is the emphasis on here? Are you trying to say that a major life decision always scares you but that's no reason for not making it? Maybe if we had more context, we'd be able to help more.

the more, the more is an expression, like proportional. chances are also an expression, meaning like "likely". https://dictionary.cambridge.org/pt/dicionario/ingles/the-chances-are https://dictionary.cambridge.org/pt/dicionario/ingles/more?q=More