An example is how Anselm believes that it is better for something to exist in both reality and understanding than in mere understanding. This is true in many situations, but there are occasions when it is better to have something that does not exist in reality, for example in cases of cancer. Imagine if cancer cells were just a product of the mind understood by everyone, but yet cancer cells did not actually exist. However, all would agree that the best thing imaginable or a god would be better in both understanding and reality. If a god is the best thing imaginable, he must exist both in reality and in the understanding, for if he were to exist only in the understanding, he would not be the best thing imaginable. If a god did not exist at all, then the concept would not exist in understanding, but it does. Therefore, a god exists in both understanding and reality. Anselm's ontological argument does not necessarily prove the existence of a god, but it actually proves the existence of the best thing imaginable, which is commonly believed to be.