The first sentence is true. The second sentence can be true but often isn’t. If 90% of the workers at a firm are worth $50,000 a year and 10% are worth $200,000 a year a union will represent the average worker, screwing the top 10%. The closer you are to the average of the members in your union the better they represent your interests. If you are far from a representative member the degree to which they will fight for your interests is markedly less.