96% of startups fail.
It's not because they build products that don't work. Rather, it's because they build products that nobody wants!
The startups that succeed are those that define the key make or break assumptions underlying their business model, create experiments and pass/fail metrics and get out of the building to test their assumptions using real people.
Speed and making as many changes based on validated learnings as possible before running out of resources is imperative to success.
Before you do this though, make sure you've completed your business model canvas first.