For startups, you need to have opinions and but be flexible about the details.
When being asked about "how much do you think people should have strong opinions about things versus putting something into the world iterating and sort of finding out whatever works and going with that?", Sam Altman said founders may want a combination of the two. You want to have a strong opinion and then be flexible about the details.
The thing he doesn't think works often are the startups that have lots of pivots that are totally unrelated to each other. There's a big difference between refinement and pivoting. It's good to start with a strong belief but with flexibility in the implementation. Like Facebook that the product itself has changed a lot along the way but the belief is still around building a social graph in an online directory. He thinks that's much better than we're just going to keep trying random ideas because we want to have a startup.
Furthermore, Sam Altman added that "the most successful people that I spend time with have strong opinions, strongly held about the future. They are willing to be convinced with new data that they are wrong, but the bar for that is fairly high."