Most people tolerate the state they live in, and try to stay out of the way of the government.
They are seldom enthusiastic about it, but they are also seldom in open rebellion. They accept that the government passes laws, and taxes them, and polices them. The fact that they accept these things is what we mean by saying that the population legitimates the state. But legitimation is not a constant. Sometimes the degree of legitimacy is relatively high, and sometimes it is relatively low.