According to your book, relationships that are most likely to last are established between people who are

According to your book, relationships that are most likely to last are established between people who are similar in dispositions and preferences.
Although the saying goes that opposites attract, it is not always the case - and even if it is, they might attract, but they don't always last long. On the other hand, people who are relatively similar with regards to their dispositions and preferences will have long-lasting relationships.