In the richest countries, for example, there will usually be more people working in the tertiary/quaternary sector than the secondary sector and primary sectors. In the poorest countries there tends to be more people working in the primary than in either the secondary or tertiary sectors.
Look at the diagram below. Based on the employment structure, which countries do you think are the richest and poorest?
In the richest country (USA), most people work in the tertiary sector. In the poorest country (Nepal), most people work in the primary sector. In Brazil, the labour force is more evenly distributed between the three sectors. Note that the quaternary sector has been included in the tertiary sector.