Olson argues you can separate "diffuse interests," the majority, from "concentrated interests," minority interests. For example, trade policy is made interest groups, lobbying the government for tariffs on imports from foreign countries. This would result in higher prices on these items. A majority of people might be opposed to this, but since the minority interests are more concentrated, they will work harder to lobby the government. The majority interests are diffuse and not organized

I believe this passage means that the reason minorities rule, is due to the fact that they are more concentrated so they are more organized and are more able to be heard by political parties and agencies that can benefit their cause. Minority groups are more concentrated to to an area where they can find other individuals who share their interest and are able to gather more supporters. Where majorities, are more scattered and are less likely to organize and get the attention and support of political parties, they are less likely to share the same interest and have the ability to get support of desired audience. 

I choose this passage because I found it interesting that minorities are most likely to be heard than majorities when the norm is the opposite, majority rules. I'm guessing this is the case because minorities are able to stuck together and come up with plans and tactics that a huge group might find it difficult to agree on.