Cpt indian contract act

Please explain the below definition of consideration

Why Promisor attains benefit and why promisee attains detriment/loss? According to this definition?

Definition Of Consideration :

“A valuable consideration in the sense of the law may consist either in some right,interest, profit or benefit accruing to the one party,(i.e Promisor) or some forbearance,determent, loss, or responsibility given, suffered or undertaken by the other…(Promisee)”