Starting a startup is too hard for one person.
5 Strategies for Building Successful Co-Founder Relationships in Startups
Josiah Humphrey

In my opinion, it depends on the person. Elon Musk’s SpaceX and Tesla were even mentioned in the beginning of this article, as being started with a sole founder. However, Musk is known for his perseverance, and especially for his 100+ hour workweeks; so, as ‘they’ (might) say, “fuel economy may vary”.