In some fields the way to succeed is to have a vision of what you want to achieve, and to hold true to it no matter what setbacks you encounter. Starting startups is not one of them. The stick-to-your-vision approach works for something like winning an Olympic gold medal, where the problem is well-defined. Startups are more like science, where you need to follow the trail wherever it leads.
Large organizations cannot be versatile. A large organization is effective through its mass rather than through its agility. Fleas can jump many times their own height, but not an elephant.