The Prince Fear Quotes

How we cite our quotes: (Chapter.Paragraph)

Quote #10

The ruler who is more afraid of his people than of foreign enemies must build fortresses; but the ruler who is more afraid of foreign enemies should do without them. (20.9)

Most of the time, Machiavelli doesn't talk about rulers being afraid of anything. So, why would a ruler be afraid of his people? (Maybe a ruler whose people hated him?)