Suppose Fred is eager to sell his condo. Victoria offers to buy it for $1,000,000, which is approximately double its market value.
When she makes the offer, Victoria says, "You have twenty-four hours in which to accept. After that, the offer terminates, and I will not purchase your condo at any price." Fred accepts the offer.
Assume, for the sake of argument, that a reasonable person in Fred's circumstances would not reject Victoria's offer. Then, if Victoria's threat never to make the offer again is improper, the contract between Victoria and Fred is.