Grant lays out three styles of building interpersonal relationships: givers, takers, and matchers.

He goes over how each strategy plays out, and tries to figure out what the optimal style is over different time horizons (I won't spoil the conclusion).

The framework of thinking about relationships in this way is useful, and highlights the importance of positive-sum people.

He attempts to position the book as if the ideas come from research and data, which I find to be over-conclusive, but his intuitions seem correct to me.