If you accept an offer, do so as soon as possible, as it can be revoked at any time until you accept it. As soon as you agree, the agreement is legally binding and cannot be modified or revoked. The reason contracts require the exchange of an item of value is to distinguish a legal agreement from a generous gift or promise made by one party to another, none of which is legally enforceable. For example, your friend mows your lawn without asking for anything, it does not count as a contract, because you have not promised a counterpart. If your friend promises to mow your lawn, but they don`t, you can`t bring an action for damages. Most business contracts fulfill the counterpart obligation with exchanged commitments. Actually doing the promised work also counts as a consideration.