There's got to be consideration on both sides of the contract. Remember, no consideration, no contract. Let's just worry about the two ways to recognize consideration for right now. You see, if consideration is part of what is needed to make a valid contract, then we've got to figure out whether or not it's there. The two important ways to determine the existence of consideration are legal and the Peppercorn Theory of Consideration.
Legal detriment means to give consideration.
Each party that is bound to a contract must be giving up something for what they are going to receive from the other party. The concept which underlies legal detriment basically says that there is no binding contract without consideration. For example, Mel's promise to drywall Jack's living room is the acceptance of a duty, which is a form of consideration. Well, now that there is consideration, there must necessarily be legal detriment. That's because legal detriment is the giving of consideration by one party to another.