Predicting Startup's Future

I've been thinking a lot about startups lately, first because I am applying for a startup accelerator program with my friend, and second because my older sister who has been working in a startup for five years finally started to generate revenue. For me, it is really difficult to see if a startup idea would work or not--naturally I thought about if there would be a statistical method to predict such thing. There must be many predictors for a startup to succeed, such as the amount of initial investment, size of the team, etc. But after seeing my sister for the past five years, I think patience and dedication are the most important factors of success. How would that be measurable, though?