Startups are best at solving the personal problems of their founders (ycopenofficehours.com)

I disagree with that sentiment. I think the best startups solve really large, difficult problems that affect the world around them.

I think it is both personal problems of founders and problems that affect the world around them. Many startups begin with someone realizing that there isn't something that they need so they create it. We also observe things in our world and see things that can be improved.